IB_Singh_-_Textbook_of_Human_Osteology,_3rd_Edition[1].pdf

TEXTBOOK OF

THIRD EDITION With Atlas of Muscle Atachments

TEXTBOOK OF

THIRD EDITION With Atlas of Muscle Atachments

INDERBIR SINGH

®

JAYPEE BROTHERS MEDICAL PUBLISHERS (P) LTD St Louis (USA) • Panama City (Panama) • New Delhi • Ahmedabad • Bengaluru • Chennai •Hyderabad • Kochi Kolkata • Lucknow • Mumbai • Nagpur

Published by Jitendar P Vij Jaypee Brothers Medical Publishers (P) Ltd Corporate Office 4838/24 Ansari Road, Daryaganj, New Delhi - 110002, India, Phone: +91-11-43574357 Fax: +91-11-43574314 Registered Office B-3 EMCA House, 23/23B Ansari Road, Daryaganj, New Delhi - 110 002, India Phones: +91-11-23272143, +91-11-23272703, +91-11-23282021, +91-11-23245672 Rel: +91-11-32558559, Fax: +91-11-23276490, +91-11-23245683 e-mail: [email protected], Website: www.jaypeebrothers.com Branches • 2/B, Akruti Society, Jodhpur Gam Road Satellite, Ahmedabad 380 015 Phones: +91-79-26926233, Rel: +91-79-32988717 Fax: +91-79-26927094, e-mail: [email protected] 202 Batavia Chambers, 8 Kumara Krupa Road, Kumara Park East, Bengaluru 560 001 • Phones: +91-80-22285971, +91-80-22382956, 91-80-22372664, Rel: +91-80-32714073 Fax: +91-80-22281761, e-mail: [email protected] • 282 IIIrd Floor, Khaleel Shirazi Estate, Fountain Plaza, Pantheon Road Chennai 600 008, Phones: +91-44-28193265, +91-44-28194897 Rel: +91-44-32972089, Fax: +91-44-28193231, e-mail: [email protected] • 4-2-1067/1-3, 1st Floor, Balaji Building, Ramkote Cross Road, Hyderabad 500 095, Phones: +91-40-66610020, +91-40-24758498 Rel:+91-40-32940929Fax:+91-40-24758499, e-mail: [email protected] No. 41/3098, B & B1, Kuruvi Building, St. Vincent Road • Kochi 682 018, Kerala, Phones: +91-484-4036109, +91-484-2395739 +91-484-2395740, e-mail: [email protected] 1-A Indian Mirror Street, Wellington Square • Kolkata 700 013, Phones: +91-33-22651926, +91-33-22276404 +91-33-22276415, Rel: +91-33-32901926, Fax: +91-33-22656075 e-mail: [email protected] • Lekhraj Market III, B-2, Sector-4, Faizabad Road, Indira Nagar, Lucknow 226 016 Phones: +91-522-3040553, +91-522-3040554, e-mail: [email protected] • 106 Amit Industrial Estate, 61 Dr SS Rao Road, Near MGM Hospital, Parel Mumbai 400 012, Phones: +91-22-24124863, +91-22-24104532, Rel: +91-22-32926896, Fax: +91-22-24160828, e-mail: [email protected] “KAMALPUSHPA” 38, Reshimbag, Opp. Mohota Science College, Umred Road • Nagpur 440 009 (MS), Phone: Rel: +91-712-3245220, Fax: +91-712-2704275 e-mail: [email protected] North America Office 1745, Pheasant Run Drive, Maryland Heights (Missouri), MO 63043, USA, Ph: 001-636-6279734 e-mail: [email protected], [email protected] Central America Office

Jaypee-Highlights Medical Publishers Inc., City of Knowledge, Bld. 237, Clayton, Panama City, Panama, Ph: (507)317-0160 Textbook of Human Osteology © 2009, Inderbir Singh All rights reserved. No part of this publication should be reproduced, stored in a retrieval system, or transmitted in any form or by any means: electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the editor and the publisher. This book has been published in good faith that the material provided by contributors is original. Every effort is made to ensure accuracy of material, but the publisher, printer and editor will not be held responsible for any inadvertent error(s). In case of any dispute, all legal matters are to be settled under Delhi jurisdiction only.

First Edition: Reprints: Second Edition: Reprints: Third Edition:

1990 1994, 1996, 1997, 2000 2002 2005, 2006 2009

ISBN 978-81-8448-300-0

Typeset at JPBMP typesetting unit Printed at

Gopsons Papers Ltd., Noida

Preface to the Third Edition

This edition of TEXTBOOK OF HUMAN OSTEOLOGY has been prepared keeping in mind the requirements of undergraduate and postgraduate students. This edition incorporates a large number of changes that should make it much more useful. 1. The entire text has been thoroughly edited and revised to improve readibility. Special effort has been made to have the text as near as possible to the relevant illustration. 2. Almost all the illustrations have been improved both with regard to appearance and to content. 3. The value of the book has been greatly increased by the addition of an entirely new part presenting an atlas of muscle attachments. I believe that students will find the atlas very useful as it will considerably reduce the burden of remembering the numerous attachments of muscles to the skeleton. I am grateful to the numerous teachers of Anatomy who have encouraged me in my book writing endeavours. I am equally grateful to the many students who have written letters, and have provided useful suggestions. The support of Mr. J.P. Vij (CMD of Jaypee Brothers) has been vital to the publication of this edition, and I am deeply indebted to him.

Rohtak 2008

INDERBIR SINGH

Author’s address: 52, Sector 1, Rohtak, 124001

Preface to the First Edition A sound knowledge of osteology continues to be fundamental to an understanding of the gross anatomy of the body. Traditionally, students in India have read osteology from large imported text books. However, in recent years, fewer and fewer students have had access to such texts. Further, with the changes in English usage in Western countries, our students are finding it increasingly difficult to follow thesse books. Most teachers of Anatomy have felt the need for a complete, well illustrated book on the subject. This book has been produced to fulfill this need.

This book has been written to meet the requirement of MBBS students. However, the matter should suffice for postgraduate students as well. For the benefit of the latter, sections on individual bones of the hands, the feet, and of the skull are included.

It is a pleasure to acknowledge the help in proof reading given by Dr. (Mrs.) Usha Dhall, and Dr. S.K. Srivastava of the Department of Anatomy, Medical College, Rohtak.

I shall welcome suggestions for improvement.

Rohtak July 1990 SINGH

INDERBIR

Contents

PART 1: INDIVIDIAL BONES OF THE BODY 1

Introduction to the skeleton ................................................................ 3

2

Bones of the Upper Limb .................................................................... 8

3

Bones of the Lower Limb .................................................................. 56

4

The Vertebral Column ..................................................................... 113

5

The Sternum and Ribs .................................................................... 134

6

The Skull as a whole ...................................................................... 145

7

Individual Bones of the Skull ......................................................... 198

PART 2: ATLAS OF MUSCLE ATTACHMENTS 8

Muscles of Upper Limb ................................................................... 233

9

Muscles of Lower Limb .................................................................. 269

10 Some Muscles of Head and Neck .................................................... 313 11 Some Muscles of Thorax and Abdomen .......................................... 326 Index ............................................................................................ 335

PART 1

Individual Bones of the body

2

3

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1 3

Introduction to the Skeleton

The human skeleton may be divided into (a) the axial skeleton (consisting of the bones of the head, neck, and trunk; and (b) the appendicular skeleton consisting of the bones of the limbs.

A preliminary look at the skull The skeleton of the head is called the skull. It is seen from the lateral side in Fig. 1.1 and from above in Fig. 1.2. The skull contains a large cranial cavity in which the brain is lodged. Just below the forehead the skull shows two large depressions, the right and left orbits, in which the eyes are lodged. In the region of the nose and mouth there are apertures that lead to the interior of the skull.

Fig. 1.1. Skull seen from the right side.

Fig. 1.2. Skull seen from above.

The skull is made up of a large number of bones that are firmly joined together. Some of these are as follows. In the region of the forehead there is the frontal bone. At the back of the head (also called the occiput) there is the occipital bone. The top of the skull, and parts of its side walls, are formed mainly by the right and left parietal bones. The region of the head just above the ears is referred to as the temple, and the bone here is the temporal bone (right or left). The bone that forms the upper jaw, and bears the upper teeth, is the maxilla. The prominence of the cheek is formed by

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the zygomatic bone. In the floor of the cranial cavity there is an unpaired bone called the sphenoid bone. The bone of the lower jaw is called the mandible. It is separate from the rest of the skull. In addition to these large bones, there are several smaller ones that will be identified when we take up the study of the skull in detail.

The vertebral column Below the skull the central axis of the body is formed by the backbone or vertebral column (Fig. 1.3). The vertebral column is made up of a large number of bones of irregular shape called vertebrae. There are seven cervical vertebrae in the neck. Below these there are twelve thoracic vertebrae that take part in forming the skeleton of the thorax. Still lower down there are five lumbar vertebrae that lie in the posterior wall of the abdomen. The lowest part of the vertebral column is made up of the sacrum, which consists of five sacral vertebrae that are fused together; and of a small bone called the coccyx. The coccyx is made up of four rudimentary vertebrae fused together. There are thus thirty three vertebrae in all. Taking the sacrum and coccyx as single bones the vertebral column has twenty six bones.

Skeleton of the thorax The skeleton of the thorax forms a bony cage that protects the heart, the lungs, and some other organs (Fig. 1.4). Behind, it is made up of twelve thoracic vertebrae. Fig. 1.3. Skull and vertebral column In front, it is formed by a bone called the sternum. The (right lateral view). sternum consists of an upper part, the manubrium; a middle part, the body; and a lower part, the xiphoid process. The side walls of the thorax are formed by twelve ribs on either side. Each rib is a long curved bone that is attached posteriorly to the vertebral column. It curves round the sides of the thorax. Its anterior end is attached to a bar of cartilage (the costal cartilage) through which it gains attachment to the sternum. This arrangement is seen typically in the upper seven ribs (true ribs). The 8th, 9th and 10th costal cartilages do not reach the sternum, but end by getting attached to the next higher cartilage (false ribs). The anterior ends of the 11th and 12th ribs are free: they are, therefore, called floating ribs.

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Fig. 1.4 A. Skeleton of the thorax as seen from the front. The bones of the shoulder girdle are also shown.

3 Fig. 1.4B. Section across thorax.

Skeleton of the Upper Limb The skeleton of each upper limb (Fig. 1.5) consists of the bones of the pectoral girdle (or shoulder girdle) that lie in close relation to the upper part of the thorax (Fig. 1.4A), and those of the free limb. The pectoral girdle consists of the collar-bone or clavicle, and the scapula. The clavicle is a rod like bone placed in front of the upper part of the thorax. Medially, it is attached to the manubrium of the sternum, and laterally to the scapula. The scapula is a triangular plate of bone placed behind the upper part of the thorax. The bone of the arm is called the humerus. There are two bones in the forearm: the bone that lies laterally (i.e., towards the thumb) is called the radius; and the bone that lies medially (i.e., towards the little finger) is called the ulna. The humerus, radius and ulna are long bones each having a cylindrical middle part called the shaft, and expanded upper and lower ends. In the wrist there are eight small, roughly cuboidal, carpal bones. The skeleton of the palm is made up of five rod like metacarpal bones, while the skeleton of the fingers (or digits) is made up of the phalanges. There are three phalanges – proximal, middle and distal – in each digit except the thumb that has only two phalanges (proximal and distal).

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The upper end of the humerus is joined to the scapula at the shoulder joint, and its lower end is joined to the upper ends of the radius and ulna to form the elbow joint. The wrist joint is formed where the lower ends of the radius and ulna meet the carpal bones. The upper and lower ends of the radius and ulna are united to one another at the superior and inferior radioulnar joints. There are numerous small joints in the hand: the intercarpal between the carpal bones themselves; the carpometacarpal between the carpal and metacarpal bones; the metacarpophalangeal between each metacarpal bone and the proximal phalanx; and the interphalangeal joints between the phalanges themselves.

Skeleton of the Lower Limb The skeleton of the lower limb consists of the bones of the pelvic girdle, and those of the free limb (Fig. 1.6). The pelvic girdle is made up of one hip bone on each side. Each hip bone is made up of three parts that are fused together. The upper expanded part of the bone is called the ilium. A small part in front (shaded in the figure) is called the pubis. The lower part of the bone is called the ischium. Anteriorly, the two pubic bones meet in the midline to form a joint called the pubic symphysis. Posteriorly, the sacrum is wedged in between the two hip bones. The hip bones and sacrum (along with the coccyx) form the bony pelvis. Fig. 1.5. Skeleton of the right upper limb. The manubrium sterni is included for orientation.

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The bones of the free part of the limb are arranged in a pattern similar to that in the upper limb. The bone of the thigh is called the femur. There are two bones in the leg. The medial of the two (lying 3 towards the great toe) is called the tibia, while the outer bone is called the fibula. The femur, tibia and fibula are long bones having cylindrical shafts with expanded upper and lower ends. In the region of the ankle, and the posterior part of the foot, there are seven roughly cuboidal tarsal bones. The largest of these is the calcaneus, which forms the heel. Next in size we have the talus. In the anterior part of the foot there are five metatarsal bones. Each digit (or toe) has three phalanges, proximal, middle and distal: however, the great toe has only two phalanges proximal and distal. The upper end of the femur fits into a deep socket in the hip bone (called the acetabulum) to form the hip joint. The lower end of the femur meets the tibia to form the knee joint. A small bone, the patella, is placed in front of the knee. The tibia and fibula are joined to each other at their upper and lower ends to form the superior and inferior tibiofibular joints. The lower ends of the tibia and fibula join the talus to form the ankle joint. Within the foot there are intertarsal, tarsometatarsal, metatarso-phalangeal and interphalangeal joints on a pattern similar to those in the hand.

Fig. 1.6. Skeleton of the pelvis and right lower limb.

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2 Bones of the Upper Limb An introduction to the skeleton of the upper limb is given in Chapter 1. Each bone is described below. The first step in the study of any bone is to orientate it as it lies in the body. To do this we have to distinguish the anterior aspect from the posterior; the upper end from the lower ; and the medial side from the lateral. Once we have this information we can find out whether the bone belongs to the right limb or the left one.

Fig. 2.1. Right clavicle seen from above.

Fig. 2.2. Right clavicle seen from below.

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The Clavicle 3 is The clavicle is a long bone having a shaft, and two ends (Figs. 2.1, 2.2). The medial end much thicker than the shaft and is easily distinguished from the lateral end which is flattened. The anterior and posterior aspects of the bone can be distinguished by the fact that the shaft (which has a gentle S-shaped curve) is convex forwards in the medial two-thirds, and concave forwards in its lateral one-third. The inferior aspect of the bone is distinguished by the presence of a shallow groove on the shaft, and by the presence of a rough area near its medial end. The side to which a clavicle belongs can be determined with the information given above. For purposes of description it is convenient to divide the clavicle into the lateral one-third which is flattened, and the medial two-thirds which are cylindrical. The lateral one-third has two surfaces, superior and inferior. These surfaces are separated by two borders, anterior and posterior. The anterior border is concave and shows a small thickened area called the deltoid tubercle. The lower surface (of the lateral one-third) shows a prominent thickening near the posterior border; this is the conoid tubercle. Lateral to the tubercle, there is a rough ridge that runs obliquely up to the lateral end of the bone, and is called the trapezoid line. The medial two-thirds of the shaft has four surfaces: anterior, posterior, superior and inferior, that are not clearly marked off from each other. The large rough area present on the inferior aspect of the bone near the medial end forms part of the inferior surface. The middle-third of the inferior aspect shows a longitudinal groove the depth of which varies considerably from bone to bone. The lateral or acromial end of the clavicle bears a smooth facet which articulates with the acromion of the scapula to form the acromioclavicular joint. The medial or sternal end of the clavicle articulates with the manubrium sterni, and also with the first costal cartilage (Fig.2.5). The articular area is smooth and extends on to the inferior surface of the bone for a short distance. The uppermost part of the sternal surface is rough for ligamentous attachments. The clavicle can be easily felt in the living person as it lies just deep to the skin in its entire extent. The sternal end of the bone forms a prominent bulge which extends above the upper border of the manubrium sterni.

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Attachments on the Clavicle A. The muscles attached to the clavicle are as follows (Figs. 2.3, 2.4) 1. The pectoralis major (clavicular head) arises from the anterior surface of the medial half of the shaft. 2. The deltoid arises from the anterior border of the lateral one-third of the shaft. 3. The sternocleidomastoid (clavicular head) arises from the medial part of the upper surface. 4. The sternohyoid (lateral part) arises from the lower part of the posterior surface just near the sternal end. 5. The trapezius is inserted into the posterior border of the lateral one-third of the shaft. 6. The subclavius is inserted into the groove on the inferior surface of the shaft.

B. Other structures attached to the clavicle are as follows. 1. The edges of the groove for the subclavius give attachment to the clavipectoral fascia. 2. The rough area above the articular surface for the manubrium sterni gives attachment to the interclavicular ligament and to the articular disc of the sternoclavicular joint. 3. The costoclavicular ligament is attached to the rough triangular area near the medial end of the inferior surface. 4. The conoid part of the coracoclavicular ligament is attached to the conoid tubercle; and its trapezoid part to the trapezoid line. 5. The articular capsules of the acromio-clavicular joint, and of the sternoclavicular joint, are attached to the margins of the articular areas for these joints.

Fig. 2.3. Right clavicle showing attachments, seen from above.

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3

Fig. 2.4. Right clavicle showing attachments, seen from below.

Ossification of the clavicle The clavicle is the first bone in the body to start ossifying. Two primary centres appear in the shaft during the 6th week of fetal life and soon fuse with each other. The sternal end ossifies from a secondary centre that appears between 15 and 20 years of age, and fuses with the shaft by the age of 25 years. An additional centre may appear in the acromion. The greater part of the clavicle is formed by intramembranous ossification. The sternal and acromial ends are preformed in cartilage.

Fig. 2.5. Medial end of clavicle seen from the medial aspect

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The Scapula The greater part of the scapula consists of a flat triangular plate of bone called the body (Figs. 2.6 to 2.8). The upper part of the body is broad, representing the base of the triangle. The inferior end is pointed and represents the apex. The body has anterior (or costal) and posterior (or dorsal) surfaces which can be distinguished by the fact that the anterior surface is smooth, but the upper part of the posterior surface gives off a large projection called the spine. At its lateral angle the bone is enlarged and bears a large shallow oval depression called the glenoid cavity which articulates with the head of the humerus. The side to which a given scapula belongs can be determined from the information given above.

Fig. 2.6. Right scapula, seen from the front.

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Fig. 2.7. Right scapula seen from behind.

3

In addition to its costal and dorsal surfaces the body has three angles: superior, inferior and lateral; and three borders: medial, lateral and superior. Arising from the body there are three processes. In addition to the spine already mentioned there is an acromion process and a coracoid process. The lateral border runs from the glenoid cavity to the inferior angle. The medial border extends from the superior angle to the inferior angle. The superior border passes laterally from

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the superior angle, but is separated from the glenoid cavity (representing the lateral angle) by the root of the coracoid process. A deep suprascapular notch is seen at the lateral end of the superior border. The costal surface lies against the posterolateral part of the chest wall. It is somewhat concave from above downwards. The dorsal surface gives attachment to the spine. The part above the spine forms the supraspinous fossa, along with the upper surface of the spine. The area below the spine forms the infraspinous fossa (along with the lower surface of the spine). The supraspinous and infraspinous fossae communicate with each other through the spinoglenoid notch that lies on the lateral side of the spine. The part of the body adjoining the lateral border is thickened to form a longitudinal bar of bone. The dorsal aspect of the scapula adjoining the lateral border is rough for muscular attachments. The glenoid cavity (Fig.2.8) is pear shaped and forms the shoulder joint along with the head of the humerus. Just below the cavity the lateral border shows a rough raised area called the infraglenoid tubercle. Immediately above the glenoid cavity there is a rough area called the supraglenoid tubercle. The region of the glenoid cavity is often regarded as the head of the scapula. Immediately medial to it there is a constriction which constitutes the neck. The spine of the scapula is triangular in form. Its anterior border is attached to the dorsal surface of the body. Its posterior border is free: it is greatly thickened and forms the crest of the spine. The medial end of the spine lies near the medial border of the scapula: this part is referred to as the root of the spine. The lateral border of the spine is free and forms the medial boundary of the spinoglenoid notch. The acromion is continuous with the lateral end of the spine. It forms a projection that is directed forwards and partly overhangs the glenoid cavity. It has a lateral border and a medial border that meet anteriorly at the tip of the acromion. The lateral border meets the crest of the spine at a sharp angle termed the acromial angle. The medial border of the acromion shows the presence of a small oval facet for articulation with the lateral end of the clavicle. The acromion has upper and lower surfaces. The coracoid process is shaped like a bent finger. The root of the process is attached to the body of the scapula just above the glenoid cavity. The lower part of the root is marked by the supraglenoid tubercle. The tip of the Fig. 2.8. Upper part of right scapula, seen from the coracoid process is directed straight forwards. lateral side.

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(To appreciate this remember that the costal surface of the body of the scapula faces anteromedially, not anteriorly. The glenoid cavity faces equally forwards and laterally.). At the point where the coracoid process bends forwards, its dorsal surface is marked by a ridge.

3 Attachments on the Scapula A. The muscles attached to the scapula are as follows (Figs. 2.9 to 2.11) 1. The deltoid takes origin from the lower border of the crest of the spine; and from the lateral margin, tip and upper surface of the acromion. 2. The trapezius is inserted into the upper border of the crest of the spine, and into the medial border of the acromion. 3. The short head of the biceps brachii arises from the (lateral part of the) tip of the coracoid process; and the long head from the supraglenoid tubercle. 4. The coracobrachialis arises from (the medial part of) the tip of the coracoid process. 5. The long head of the triceps arises from the infraglenoid tubercle. 6. The pectoralis minor is inserted into the superior aspect of the coracoid process. 7. The inferior belly of the omohyoid arises from the upper border near the suprascapular notch. 8. The subscapularis arises from the whole of the costal surface, but for a small part near the neck. 9. The serratus anterior is inserted on the costal surface along the medial border.

Fig. 2.9. Right scapula, showing attachments, seen from the front.

The first digitation of the muscle is inserted from the superior angle to the root of the spine. The next two or three digitations are inserted into a narrow line along the medial border. The

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Fig. 2.10. Right scapula, showing attachments, seen from behind.

lower 4 or 5 digitations are inserted into a large triangular area over the inferior angle. 10. The supraspinatus arises from the medial two-thirds of the supraspinous fossa, including the upper surface of the spine. 11. The infraspinatus arises from the greater part of the infraspinous fossa, but for a part near the lateral border and a part near the neck. 12. The teres minor arises from the upper two-thirds of the rough strip on the dorsal surface, near the lateral border. There is a gap in the area of origin for passage of the circumflex scapular vessels. 13. The teres major arises from the lower one-third of the rough strip along the dorsal aspect of the lateral border. The area is wide and extends over the inferior angle. 14. The levator scapulae is inserted into a narrow strip along the dorsal aspect of the medial border, extending from the superior angle to the level of the root of the spine.

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15. The rhomboideus minor is inserted into the dorsal aspect of the medial border, opposite the root of the spine. 16. The rhomboideus major is inserted into the dorsal aspect of the medial border, from the root of the spine to the inferior angle.

3

17. The latissimus dorsi receives a small slip from the dorsal surface of the inferior angle.

B. The ligaments attached to the scapula are as follows 1. The capsule of the shoulder joint and the glenoidal labrum are attached to the margins of the glenoid cavity. In its upper part the attachment of the capsule extends above the supraglenoid tubercle so that the origin of the long head of the biceps is within the capsule.

Fig. 2.11. Right scapula, showing attachments, seen from the lateral side

2. The capsule of the acromioclavicular joint is attached to the margins of the facet for the clavicle. 3. The coracoacromial ligament is attached as follows. Its anteromedial end is attached to the lateral border of the coracoid process; and its lateral end to the medial aspect of the tip of the acromion just in front of the clavicular facet. 4. The coracoclavicular ligament is attached to the coracoid process: the trapezoid part on its superior aspect, and the conoid part near the root. 5. The suprascapular ligament bridges across the suprascapular notch and converts it into a foramen which transmits the suprascapular nerve. The suprascapular vessels lie above the ligament. Ossification of the scapula The scapula usually has eight centres of ossification. 1. A centre appears in the body during the 8th week of fetal life. The spine is ossified by extension from this centre. 2. The greater part of the coracoid process is ossified from a centre that appears in the first year. About the age of puberty a second centre appears in the root of the coracoid process. This is called the subcoracoid centre. Extension of ossification from this centre is responsible for forming the upper part of the glenoid cavity.

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3. At about the age of puberty two centres appear in the acromion, and one each in the lower part of the glenoid cavity, the inferior angle and the medial border. 4. The subcoracoid centre fuses with the body by the 15th year. Other centres fuse with the body by the 20th year.

The Humerus The humerus is a long bone. It has a cylindrical central part called the shaft, and enlarged upper and lower ends (Figs. 2.12, 2.13). The upper end is easily distinguished from the lower by the presence of a large rounded head. The medial and lateral sides can be distinguished by the fact that the head is directed medially. The anterior aspect of the upper end shows a prominent vertical groove called the intertubercular sulcus. The side to which a given bone belongs can be determined from the information given above. The head is rounded and has a smooth convex articular surface. It is directed medially, and also somewhat backwards and upwards. It forms the shoulder joint along with the glenoid cavity of the scapula. It may be noted that the articular area of the head is much greater than that of the glenoid cavity. In addition to the head, the upper end of the humerus shows two prominences called the greater and lesser tubercles (or tuberosities). These two tubercles are separated by the intertubercular sulcus (also called the bicipital groove): this is the vertical groove on the anterior aspect of the upper end mentioned above. The lesser tubercle lies on the anterior aspect of the bone medial to the sulcus, between it and the head. It has a smooth upper part and a rough lower part. The greater tubercle is placed on the lateral aspect of the upper end and parts of it can, therefore, be seen from both the anterior and posterior aspects. Its anterior part forms the lateral boundary (or lip) of the intertubercular sulcus. The tubercle shows three areas (or impressions) where muscles are attached (Fig.2.14). The uppermost of these is placed on the superior aspect, the lowest on the posterior aspect, and the middle is in between them. There are two distinct regions of the upper end of the humerus that are referred to as the neck. The junction of the head with the rest of the upper end is called the anatomical neck, while the junction of the upper end with the shaft is called the surgical neck.

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The shaft of the humerus has three borders: anterior, medial and lateral. These are readily identified in the lower part of the bone (Fig. 2.15B). When traced upwards the anterior border 3 becomes continuous with the anterior margin of the greater tubercle (or crest of the greater tubercle, or lateral lip of the intertubercular sulcus). The medial border is indistinct in its upper part, but it can be traced to the lower end of the lesser tubercle, and to its sharp lateral margin (crest of the lesser tubercle, or medial lip of the intertubercular sulcus). The lower part of the lateral border can be seen from the front, but its upper part runs upwards on the posterior aspect of the bone. The three borders divide the shaft into three surfaces. The anterolateral surface lies between the anterior and lateral borders; the anteromedial surface between the anterior and medial borders, and the posterior surface between the medial and lateral borders.

Fig. 2.12. Right humerus seen from the front.

Note that because of the convergence of the anterior and medial borders in the upper part of the bone, the anteromedial surface becomes continuous with the intertubercular sulcus (Figs. 2.12, 2.15A), and part of the posterior surface can be seen from the front. Similarly, because of the medial inclination of the lateral border in its upper part (see Fig. 2.13) part of the anterolateral surface can be seen from behind. We may now note certain additional features of the shaft. The anterolateral surface has a V-shaped rough area called the deltoid tuberosity which is present near the middle of this surface. The anterior limb of the tuberosity lies along

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the anterior border of the shaft, while the posterior limb lies above the lower part of the radial groove (see below). The medial border also bears a roughened strip near it middle. When the shaft is observed from behind we see that its upper part is crossed by a broad and shallow radial groove which runs downwards and laterally across the posterior and anterolateral surfaces. The radial groove interrupts the lateral border of the shaft. The part of the border below the groove is indistinct; the part above the groove is also not well marked, but can be traced to the posterior part of the greater tuberosity. The upper margin of the radial groove is formed by a roughened ridge that runs obliquely across the shaft: the lower end of the ridge is continuous with the posterior limb of the deltoid tuberosity. The lower end of the humerus is irregular in shape and is also called the condyle. The lowest parts of the medial and lateral borders of the humerus form sharp ridges that are called the medial and lateral supracondylar ridges respectively. Their lower ends terminate in two prominences called the medial and lateral epicondyles. The medial epicondyle is the larger of the two. Between the two epicondyles the lower end presents an irregular shaped articular surface which is divisible into medial and lateral parts. The lateral part is rounded and is called the capitulum. It articulates with the head of the radius. The medial part of the articular surface is shaped like a pulley and is called the trochlea. It is separated from the capitulum by a faint groove. The medial margin of the trochlea projects downwards much below the level of the capitulum, and of the epicondyles. The trochlea articulates with the upper end (trochlear notch) of the ulna. The anterior aspect of the lower end of the humerus shows two depressions: one just above the capitulum and another above the trochlea. The

Fig. 2.13. Right humerus seen from behind.

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Fig. 2.14. Upper end of right humerus seen from above.

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depression above the capitulum is called the radial fossa and that above the trochlea is called the coronoid fossa (Fig. 2.12). Parts of the head of the radius and of the coronoid process of the ulna lie in these depressions when the elbow is 3 fully flexed. Another depression is seen above the trochlea on the posterior aspect of the lower end (Fig. 2.13). This depression is called the olecranon fossa as it lodges the olecranon process of the ulna when the elbow is fully extended.

Attachments on the Humerus A. The muscles attached to the humerus are as follows (Figs.2.16 to 2.18) 1. The supraspinatus is inserted into the upper impression on the greater tubercle. 2. The infraspinatus is inserted into the middle impression on the greater tubercle. 3. The teres minor is inserted into the lower impression on the greater tubercle. 4. The subscapularis is inserted into the lesser tubercle. 5. The pectoralis major is inserted into the lateral lip of the intertubercular sulcus. 6. The latissimus dorsi is inserted into the floor of the intertubercular sulcus. 7. The teres major is inserted into the medial lip of the intertubercular sulcus. Of the three insertions into the intertubercular sulcus that of the pectoralis major is the most extensive, and that of the latissimus dorsi is the shortest. Fig. 2.15. Transverse sections through the shaft of the humerus. A. near upper end. 8. The deltoid is inserted into the deltoid B. at its middle. C. near lower end. tuberosity. The sections are viewed from below.

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9. The coracobrachialis is inserted into the rough area on the middle of the medial border. 10. The brachialis arises from the lower halves of the anteromedial and anterolateral surfaces of the shaft. Part of the area of origin extends onto the posterior aspect. 11. The pronator teres (humeral head) arises from the anteromedial surface, near the lower end of the medial supracondylar ridge. 12. The brachioradialis arises from the upper two -thirds of the lateral supracondylar ridge. 13. The extensor carpi radialis longus arises from the lower one-third of the lateral supracondylar ridge. 14. The superficial flexor muscles of the forearm arise from the anterior aspect of the medial epicondyle. This origin is called the common flexor origin. 15. The common extensor origin for the superficial extensor muscles of the forearm is located on the anterior aspect of the lateral condyle. 16. The lateral head of the triceps arises from the oblique ridge on the upper part of the posterior surface, just above the radial groove. The medial head of the muscle arises from the posterior surface below the radial groove. The upper end of the area of origin extends on to the anterior aspect of the shaft. 17. The anconeus arises from the posterior surface of the lateral epicondyle. Fig. 2.16. Right humerus, showing attachments, seen from the front.

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B. Other structures attached to the humerus are as follows 1. The capsular ligament of the shoulder joint is attached on the anatomical neck 3 of except on the medial side where the line attachment dips down by about a centimetre to include a small area of the shaft within the joint cavity. The line of attachment of the capsule is interrupted at the intertubercular sulcus to provide an aperture through which the tendon of the long head of the biceps leaves the joint cavity. 2. The capsular ligament of the elbow joint is attached to the lower end of the bone. The line of attachment reaches the upper limits of the radial and coronoid fossae, anteriorly, and of the olecranon fossa posteriorly so that these fossae lie within the joint cavity. Medially, the line of attachment passes between the medial epicondyle and the trochlea. On the lateral side it passes between the lateral epicondyle and the capitulum. 3. The medial and lateral supracondylar ridges give attachment to the medial and lateral intermuscular septa. 4. The medial and lateral epicondyles give attachment to the ulnar and radial collateral ligaments respectively.

Fig. 2.17. Right humerus, showing attachments seen from behind.

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Important relations 1. The intertubercular sulcus lodges the tendon of the long head of the biceps brachii. The ascending branch of the anterior circumflex humeral artery also lies in this sulcus. 2. The surgical neck of the bone is related to the axillary nerve and to the anterior and posterior circumflex humeral vessels. 3. The radial nerve and the profunda brachii vessels lie in the radial groove between the attachments of the lateral and medial heads of the triceps.

Fig. 2.18. Upper end of right humerus, showing attachments, seen from above.

4. The ulnar nerve crosses behind the medial epicondyle.

Ossification of the humerus 1. A primary centre appears in the shaft during the 8th fetal week. The greater part of the bone is formed from this centre. 2. A secondary centre for the head appears early in the first year; for the greater tubercle in the second year; and for the lesser tubercle in the fifth year. These three parts fuse with each other in the sixth year to form a single epiphysis for the upper end which fuses with the shaft around 18 to 20 years of age. 3. At the lower end a centre appears in the capitulum during the first year; in the medial part of the trochlea in the ninth or tenth year; and in the lateral epicondyle around the twelfth year. These fuse to form a single epiphysis which fuses with the shaft around 15 years of age. A separate centre appears in the medial epicondyle around the fifth year; and fuses with the shaft about the twentieth year.

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The Radius The radius is a long bone having a shaft and two ends: upper and lower (Figs. 2.19 to 2.23). The upper end bears a disc shaped head. In contrast the lower end is much enlarged. The lateral and medial sides of the bone can be distinguished by examining the shaft which is convex laterally and has a sharp medial (or interosseous) border. The anterior and posterior aspects of the bone may be identified by looking at the lower end: it is smooth anteriorly, but the posterior aspect is marked by a number of ridges and grooves. The side to which a given radius belongs can be determined from the information given above.

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The upper end of the bone consists of a head, a neck and a tuberosity. The head is disc shaped. Its upper surface is slightly concave and articulates with the capitulum of the humerus. The circumference of the head (representing the edge of the disc) is also smooth and articular. Medially it articulates with a notch on the ulna: the remaining part is enclosed by the annular ligament (Fig. 2.21). This joint between the radius and ulna is the superior radioulnar joint. The region just below the head is constricted to form the neck. Just below the medial part of the neck there is an elevation called the radial tuberosity. The tuberosity is rough in its posterior part, and is smooth anteriorly. The shaft of the radius has three borders (anterior, posterior, and interosseous) and three surfaces (anterior, posterior and lateral) (Fig. 2.22). The interosseous or medial border is easily identified as it forms a sharp ridge which extends from just below the tuberosity to the lower end of the shaft. Near the lower end this border forms the posterior margin of a small triangular area. The anterior border begins at the radial tuberosity and runs downwards and laterally across the anterior aspect of the shaft. This part of the anterior border is

Fig. 2.19. Right radius seen from the front.

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Fig. 2.21. Scheme to show the relationship of the head of the radius to the ulna and to the annular ligament.

Fig. 2.22. Transverse section across the middle of the shaft of the radius to show its borders and surfaces.

Fig. 2..20. Right radius seen from behind.

called the anterior oblique line. It then runs downwards and forms the lateral boundary of the smooth anterior aspect of the lower part of the shaft. The upper part of the posterior border runs downwards and laterally from the posterior part of the tuberosity. The lower part of the posterior border runs downwards along the middle of the posterior aspect of the shaft to the lower end. The anterior surface lies between the interosseous and anterior borders; the posterior surface between the interosseous and posterior borders; and the lateral surface between the anterior and posterior borders. In the upper part of the bone the lateral surface expands into a wide triangular area as it extends on to the anterior and posterior aspects of the bone. The lateral surface shows a rough area near the middle (and most convex) part of the shaft. The lower end of the radius has anterior, lateral and posterior surfaces continuous with the

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corresponding surfaces of the shaft. In addition it has a medial surface and an inferior surface. The lateral surface is prolonged downwards as a projection called the styloid process. The medial aspect of the lower end has an articular area called the ulnar notch (Fig. 2.23A). It articulates with the lower end of the ulna to form the inferior radioulnar joint. Just above the notch there is a triangular area bounded posteriorly by the interosseous border. The posterior aspect of the lower end is marked by a number of vertical grooves separated by ridges. The most prominent ridge is called the dorsal tubercle which is placed roughly midway between the medial and lateral aspects of the lower end. Immediately medial to the tubercle there is a narrow oblique groove, and still more medially there is a wide shallow groove. The area lateral to the dorsal tubercle shows two grooves separated by a ridge. The inferior surface of the lower end is articular. It takes part in forming the wrist joint. It is subdivided into a medial quadrangular area that articulates with the lunate bone, and a lateral triangular area that articulates with the scaphoid bone.

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Fig. 2.24. Right radius, showing attachments seen from the front.

Fig. 2.23. Lower end of the right radius seen: A. From the medial side. B. From below.

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Attachments on the Radius A. The following muscles are inserted into the radius (Figs. 2.24 to 2.27) 1. The biceps brachii is inserted into the rough posterior part of the radial tuberosity. 2. The supinator is inserted into the upper part of the lateral surface. The area of insertion extends on to the anterior and posterior aspects of the shaft. 3. The pronator teres is inserted into the rough area on the middle of the lateral surface, at the point of maximum convexity of the shaft. 4. The brachioradialis is inserted into the lowest part of the lateral surface just above the styloid process. 5. The pronator quadratus is inserted into the lower part of the anterior surface, and into the triangular area on the medial side of the lower end.

B. The following muscles take origin from the radius 1. The flexor digitorum superficialis (radial head) arises from the upper part of the anterior border (oblique line). 2. The flexor pollicis longus arises from the upper two-thirds of the anterior surface. 3. The abductor pollicis longus arises from the upper part of the posterior surface. 4. The extensor pollicis brevis arises from a small area on the posterior surface below the area for the abductor pollicis longus.

Fig.2.25. Right radius, showing attachments seen from behind.

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Fig. 2.27. Lower end of right radius seen from below. The related tendons are shown. Fig. 2.26. Lower end of right radius, showing attachments, seen from the medial side.

C. Other structures attached to the radius are as follows 1. The articular capsule of the wrist joint is attached to the anterior and posterior margins of the lower end and to the styloid process. Note that the articular capsule of the elbow joint does not have a direct attachment to the upper end of the radius. 2. The articular disc of the inferior radioulnar joint is attached to the lower border of the ulnar notch. 3. The interosseous membrane is attached to the lower three fourths of the interosseous border. 4. The oblique cord is attached just below the radial tuberosity. 5. The extensor retinaculum is attached to the lower part of the anterior border (which is sharp here). In figure 2.24 the attachment is shown in purple line.

D. Tendons related to the lower end of the radius. 1. The shallow groove behind the medial part of the lower end lodges the tendons of the extensor digitorum and of the extensor indicis. 2. The oblique groove medial to the dorsal tubercle is occupied by the tendon of the extensor pollicis longus. 3. The groove lateral to the dorsal tubercle is occupied by the tendons of the extensor carpi radialis longus and brevis. 4. The lateral aspect of the lower end of the radius is crossed by the tendon of the abductor pollicis longus and of the extensor pollicis brevis.

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Ossification of the radius 1. A primary centre appears in the shaft during the 8th week of fetal life. 2. A secondary centre appears in the lower end in the first year and joins the shaft around 18 years of age. 3. A secondary centre appears in the head of the bone during the 4th or 5th year and fuses with the shaft around the 16th year. 4. Occasionally the radial tuberosity may ossify from a separate centre.

The Ulna The ulna has a shaft, an upper end and a lower end (Figs. 2.28 to 2.31). The upper end is large and irregular, while the lower end is small. The upper end has a large trochlear notch on its anterior aspect. The medial and lateral sides of the bone can be distinguished by examining the shaft (Fig. 2.31): its lateral margin is sharp and thin, while its medial side is rounded. The side to which an ulna belongs can be determined from these facts. The upper end of the ulna consists of two prominent projections called the olecranon process and the coronoid process. When seen from behind the olecranon process appears to be a direct upward continuation of the shaft and forms the uppermost part of the ulna. The coronoid process projects forwards from the anterior aspect of the ulna just below the olecranon process (Fig. 2.30). The trochlear notch covers the anterior aspect of the olecranon process and the superior aspect of the coronoid process. It takes part in forming the elbow joint and articulates with the trochlea of the humerus. The upper and lower parts of the notch may be partially separated from each other by a non-articular area. The trochlear notch is also divisible into medial and lateral areas corresponding to the medial and lateral flanges of the trochlea. In addition to its anterior surface which forms the upper part of the trochlear notch the olecranon process has superior, posterior, medial and lateral surfaces (Fig. 2.28). When viewed from the lateral side the uppermost part of the olecranon is seen projecting forwards beyond the rest of the process (Fig. 2.30). The coronoid process has an upper surface which forms the lower part of the trochlear notch. In addition it has anterior, medial and lateral surfaces. The anterior surface is triangular. Its lower part shows a rough projection called the tuberosity of the ulna. The medial margin of the anterior surface is sharp and shows a small tubercle at its upper end. The upper part of the lateral surface of the coronoid process shows a concave articular facet called the radial notch

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Fig. 2.28. Right ulna seen from the front.

Fig. 2.29. Right ulna seen from behind.

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(Fig. 2.30). The radial notch articulates with the head of the radius forming the superior radio-ulnar joint. The bone shows a depression just below the radial notch. The posterior border of this depression is formed by a ridge called the supinator crest (Fig. 2.30). The lower end of the ulna consists of a disc-like head and a styloid process. The head has a circular inferior surface (Fig. 2.36). This surface is separated from the cavity of the wrist joint by an articular disc. The head has another convex articular surface on its lateral side: this surface articulates with the ulnar notch of the radius to form the inferior radioulnar joint. The styloid process is a small downward projection that lies on the posteromedial aspect of the head. Between the styloid process and the head the posterior aspect is marked by a vertical groove. It is of importance to note that in the intact body the tip of the styloid process of the ulna lies at a higher level than the styloid process of the radius.

Fig. 2.30. Upper part of right ulna seen from the lateral side.

The shaft of the ulna has a sharp lateral or interosseous border, and less prominent anterior and posterior borders (Fig. 2.31). It has anterior, posterior and medial surfaces. The upper part of the interosseous border is continuous with the supinator crest mentioned above. Its central part forms a prominent ridge on the lateral aspect of the shaft. The lower part of this border is indistinct and ends on the lateral side of the head. The anterior border begins at the tuberosity of the ulna (Fig. 2.28) and runs downwards. Near its lower end it curves backwards to end in front of the styloid process. The posterior border begins at the apex of the triangular area on the posterior aspect of the olecranon process (Fig. 2.29) and ends at the styloid process. The anterior surface of the ulna lies between the interosseous and anterior borders. Its lower part shows an oblique ridge that runs downwards and medially from the interosseous border. The medial surface lies between the anterior and posterior borders. The posterior surface is bounded by the interosseous and posterior borders. It is marked by two lines that divide it into three areas. The upper of these lines runs obliquely downwards and medially across the upper part of the surface. It starts at the posterior end of the radial notch and terminates by joining the posterior border. The part of the posterior surface above the line is triangular. The part below the oblique line is subdivided into medial and lateral Fig. 2.31. T.S. across the middle of the parts by a vertical ridge. shaft of the ulna to show its surfaces and borders.

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Attachments on the Ulna A. The muscles inserted into the ulna are as follows (Figs. 2.32 to 2.37). 1. The brachialis is inserted into the anterior surface of the coronoid process including the tuberosity.

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2. The triceps is inserted into the posterior part of the superior surface of the olecranon process (Figs. 2.35, 2.37). 3. The anconeus is inserted into the lateral aspect of the olecranon process and into the upper one fourth of the posterior surface of the shaft.

B. The muscles taking origin from the ulna are as follows. 1. The flexor digitorum profundus arises from the upper three-fourths of the anterior and medial surfaces. The origin extends upwards on to the medial surfaces of the coronoid and olecranon processes. The muscle also takes origin from the posterior border through an aponeurosis common to it, the flexor carpi ulnaris and the extensor carpi ulnaris. 2. The supinator arises from the supinator crest and from the triangular area in front of it. 3. The flexor pollicis longus (occasional ulnar head) arises from the lateral border of the coronoid process. 4. The flexor digitorum superficialis (ulnar head) arises from the tubercle at the upper end of the medial margin of the coronoid process. 5. The pronator teres (ulnar head) arises from the medial margin of the coronoid process. 6. The pronator quadratus arises from the oblique ridge on the lower part of the anterior surface of the shaft.

Fig. 2.32. Right ulna, showing attachments, seen from the front.

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Fig. 2.33. Upper end of right ulna showing attachments, seen from the lateral side.

Fig. 2.34. Upper end of right ulna, showing attachments, seen from the medial side.

7. The flexor carpi ulnaris (ulnar head) arises from the medial side of the olecranon process (Fig. 2.34), and from the upper two-thirds of the posterior border through an aponeurosis common to it, the extensor carpi ulnaris and the flexor digitorum profundus. 8. The extensor carpi ulnaris (ulnar head) arises from the posterior border by an aponeurosis common to it, the flexor carpi ulnaris and the flexor digitorum profundus. 9. The posterior surface of the ulna is divided into medial and lateral parts by a vertical ridge. The lateral part lies between the vertical ridge and the

Fig. 2.35. Right ulna, showing attachments, seen from behind.

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interosseous border. This part of the posterior surface may be divided into four parts: (a) The uppermost part gives origin to the abductor pollicis longus.

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(b) The next part gives origin to the extensor pollicis longus. (c) The third part gives origin to the extensor indicis

Fig. 2.36. Lower end of right ulna seen from below;

(d) The lowest part is devoid of attachments.

C. Other attachments on the ulna are as follows. 1. The interosseous membrane is attached to the interosseous border.

Fig. 2.37. Olecranon seen from above.

2. The oblique cord is attached to the lateral side of the tuberosity (Fig. 2.32). 3. The capsular ligament of the elbow joint is attached to the margins of the trochlear notch (i.e., to the coronoid and olecranon processes). 4. The annular ligament is attached to the anterior and posterior borders of the radial notch (Figs. 2.32 and 2.33). 5. The ulnar collateral ligament of the wrist is attached to the styloid process. 6. The articular disc of the inferior radio-ulnar joint is attached by its apex to a small rough area just lateral to the styloid process (Fig. 2.36). D. The tendon of the extensor carpi ulnaris lies in a groove on the posterior aspect of the lower end of the ulna. Ossification of the ulna 1. A primary centre appears in the shaft in the 8th fetal week and forms the greater part of the ulna. 2. A centre for the lower end appears around the 5th or 6th year and joins the shaft by the 18th year. 3. The greater part of the olecranon is ossified by extension from the primary centre. The proximal part of the process is ossified from two centres that appear about the 10th year and join the shaft around the 15th year.

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The Skeleton of the Hand The skeleton of the hand consists of the bones of the wrist, the palm, and of the digits. The skeleton of the wrist consists of eight, small, roughly cuboidal carpal bones. The skeleton of the palm is made up of five metacarpal bones. These are miniature ‘long’ bones. The skeleton of the fingers is made up of the phalanges. There are three phalanges (proximal, middle and distal) in each digit except the thumb which has only two phalanges (proximal and distal).

THE CARPAL BONES The carpal bones are arranged in two rows, proximal and distal (Figs. 2.38 to 2.47). The proximal row is made up (from lateral to medial side) of the scaphoid, lunate, triquetral and pisiform

Fig. 2.38. Skeleton of the hand, seen from the palmar aspect.

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Fig. 2.39. Right carpus, seen from the front.

bones. The distal row is made up (from lateral to medial side) of the trapezium, trapezoid, capitate and hamate bones. The carpal bones of the proximal row (except the pisiform) take part in forming the wrist joint. The distal row of carpal bones articulate with the metacarpal bones. Each carpal bone articulates with neighbouring carpal bones to form intercarpal joints. We will now take up the consideration of individual bones of the hand. Many of the features to be described can be identified in the articulated hand (Fig. 2.38), and these are the ones that need to be known for understanding the attachments of various structures. Some further details can be seen only on isolated bones. Most teachers of anatomy no longer expect undergraduate students to be able to assign individual bones to the right or left side. This information is included for the use of postgraduate students, or for the occasional undergraduate student who may wish to use it.

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The Scaphoid Bone The scaphoid bone can be distinguished because of its distinctive boat-like shape (Figs. 2.38 to 2.40). The orientation of the bone is shown in Figs. 2.38 and 2.39. In these figures note that the proximal part of the bone is covered by a large, convex, articular surface for the radius. Distally and laterally the palmar surface of the bone bears a projection called the tubercle. The medial surface of the scaphoid articulates with the lunate bone (proximally) and with the capitate (distally). The distal surface of the scaphoid articulates with the trapezium (laterally) and with the trapezoid bone (medially). The side to which a given scaphoid bone belongs can be determined as follows: 1. The proximal side is distinguished from the distal as it bears a large convex facet for the radius. The tubercle is placed distally. 2. The palmar aspect can be distinguished from the dorsal as it bears the tubercle (on its distal and lateral part). The dorsal surface is narrower than the palmar surface. 3. The medial and lateral aspects can also be distinguished by looking at the tubercle which lies laterally. The medial aspect bears a flat semilunar facet for the lunate bone, and a concave facet for the capitate bone.

Fig. 2.40. Right scaphoid bone. A. Palmar aspect. B. Medial aspect. C. Distal aspect.

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The Lunate Bone The lunate bone can be distinguished because it is shaped like a lunar crescent (Figs. 2.38, 2.39, 2.41). Note the following in figures 2.38 and 2.39.

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Proximally, the bone has a convex articular facet that takes part in forming the wrist joint. The bone articulates laterally with the scaphoid; medially with the triquetral; and distally with the capitate. Between the areas for the capitate and for the triquetral the lunate may articulate with the hamate bone. The side to which a given lunate bone belongs can be determined with the help of the following information: 1. The palmar surface is larger than the dorsal surface. Both these surfaces are non-articular and rough.

Fig. 2.41. Right lunate bone. A. Lateral aspect. B. Medial aspect

2. The proximal aspect bears a convex facet (for the radius) while the distal aspect bears a concave facet (for the capitate). 3. The medial surface bears a square facet (for the triquetral) while the lateral surface bears a semilunar facet (for the scaphoid bone).

The Pisiform Bone This bone is easily distinguished as it is shaped like a pea (Figs. 2.38, 2.39, 2.42). Its dorsal aspect bears a single facet for articulation with the triquetral bone. It is difficult to determine the side of this bone. Fig. 2.42. Right pisiform bone, dorsal aspect

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The Triquetral Bone The triquetral bone can be distinguished from other carpal bones by the fact that it is a small roughly cuboidal bone (Figs. 2.38, 2.39, 2.43). It has palmar, dorsal, proximal, distal, medial and lateral surfaces. Note the following in figures 2.38 and 2.39. The distal part of its palmar surface articulates with the pisiform bone. The medial surface is directed as much proximally as medially. It bears a slightly convex surface which takes part in forming the wrist joint: it comes into contact with the articular disc of the inferior radioulnar joint. Its lateral surface is also directed distally. It articulates with the hamate bone. The proximal surface is also directed laterally. It articulates with the lunate bone. The side to which a given triquetral bone belongs can be determined with the help of the following information: 1. The palmar aspect bears a discrete oval facet (for the pisiform bone). The dorsal aspect is non-articular.

Fig. 2.43 Right triquetral bone. A. Palmar aspect. B. Proximal aspect. C. Lateral aspect

2. The distal aspect can be distinguished from the proximal aspect because of the fact that the facet for the pisiform is located on the distal part of the palmar surface. 3. The medial surface bears a convex facet (for the wrist joint) while the lateral surface bears a concavo-convex facet (for the hamate bone).

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The Trapezium This bone can be distinguished because it bears a thick prominent ridge on its palmar aspect (Figs. 2.38, 2.39, 2.44). This ridge is called the tubercle.

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From figures 2.38 and 2.39 note that the trapezium articulates proximally and medially with the scaphoid; distally and laterally with the first metacarpal bone; medially with the trapezoid bone; and distally and medially with the base of the second metacarpal bone. The side to which a given trapezium belongs can be found using the following information: 1. The palmar surface is distinguished from the dorsal as it bears the tubercle. 2. The medial and lateral aspects can also be distinguished by examining the palmar surface: there is a deep groove on the medial side of the tubercle. 3. The distal surface bears a concavoconvex facet (for the first metacarpal), while the proximal surface bears a small concave facet (for the scaphoid).

Fig. 2.44. Right trapezium. A. Palmar aspect. B. Distal and lateral aspect. C. Proximal and medial aspect.

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Fig. 2.45. Right trapezoid bone. A. Lateral aspect. B. Medial aspect.

The Trapezoid Bone This bone can be distinguished from other carpal bones because of its small size and its irregular shape. Its shape resembles that of a shoe (Figs. 2.38, 2.39, 2.45). From figures 2.38 and 2.39 note that the trapezoid articulates distally with the base of the 2nd metacarpal bone, laterally with the trapezium, medially with the capitate, and proximally with the scaphoid. The side to which a given trapezoid belongs can be determined as follows: 1. The palmar surface is much smaller than the dorsal aspect (The dorsal aspect corresponds to the sole of the shoe). 2. The distal aspect bears a concavo-convex facet for the base of the 2nd metacarpal bone. (The toe of the shoe is directed distally). 3. The medial and lateral sides can be distinguished by the fact that a rough, non-articular, strip passes dorsally from the lateral (and distal) part of the palmar surface.

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The Capitate Bone The capitate bone is easily recognized as it is the largest carpal bone, and bears a rounded head at one end (Figs. 2.38, 2.39, 2.46).

3

From figures 2.38 and 2.39 it will be seen that the capitate lies right in the middle of the carpus. Proximally, it articulates with the lunate bone, the rounded head fitting into a socket formed by the lunate and scaphoid bones. Distally the capitate bone articulates mainly with the third metacarpal bone, but it also articulates with the second and fourth metacarpal bones. Its lateral aspect articulates with the scaphoid (proximally) and with the trapezoid (distally). Medially it articulates with the hamate bone. The side to which a given capitate bone belongs can be determined using the following information: 1. The rounded head is proximal. The distal surface is triangular. 2. The dorsal surface is larger than the palmar surface. Both are rough. 3. The medial aspect bears a large facet for the hamate. The lateral surface has a smaller facet for the trapezoid bone. It is also useful to know that the articular surface on the head extends considerably on to the lateral aspect (this part being for articulation with the scaphoid bone).

Fig. 2.46. Right capitate bone. A. Palmar aspect. B. Lateral aspect. C. Medial aspect. The two facets for the hamate are often fused.

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The Hamate Bone The hamate is easy to recognize as it has a prominent hook-like process attached to the distal and medial part of its palmar aspect (Figs. 2.38, 2.39, 2.47). From figures 2.38 and 2.39 note that when viewed from the palmar aspect the hamate is triangular in shape, the apex of the triangle being directed proximally. The apex may articulate with the lunate bone. Distally the hamate articulates with the 4th and 5th metacarpal bones. Medially and proximally the hamate articulates with the triquetral bone, and laterally with the capitate. The side to which a particular hamate bone belongs can be found by noting the following facts about the hook: 1. The hook is attached to the palmar surface. 2. The concavity of the hook is directed laterally. 3. The hook is attached near the distal end of the palmar aspect. The distal aspect bears a facet that is divided into two parts by a ridge, for articulation with the 4th and 5th metacarpal bones.

Fig. 2.47. Right hamate bone. A. Anterior aspect. B. Proximal and medial aspect. C. Distal aspect. D. Lateral aspect.

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The Carpal Tunnel The carpal bones are so arranged that the dorsal, medial and lateral surfaces of the carpus form one convex surface. On the other hand the palmar surface is deeply concave with overhanging medial and lateral projections. This concavity is converted into the carpal tunnel by a band of fascia called the flexor retinaculum (Fig. 2.48). The retinaculum is attached, medially to the pisiform bone and to the hook of the hamate; and laterally to the tubercle of the scaphoid and to the tubercle of the trapezium.

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Fig. 2.48. Schematic section across the distal row of carpal bones.

THE METACARPAL BONES The hand has five metacarpal bones (Figs. 2.38, 2.49 to 2.55). They are numbered from lateral to medial side so that the bone related to the thumb is the first metacarpal, and that related to the little finger is the fifth. Each metacarpal is a miniature long bone having a shaft, a distal end and a proximal end. The distal end forms a rounded head. It bears a large convex articular surface for articulation with the proximal phalanx of the corresponding digit. The shaft is triangular in cross section (Fig. 2.50) and has medial, lateral and dorsal surfaces. The bases (or proximal ends) of the metacarpal bones are irregular in shape. They articulate with the distal row of carpal bones.

Fig. 2.49. Carpal and metacarpal bones of the right hand as seen from the front.

Fig. 2.50. Transverse section across the shaft of a metacarpal bone.

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Fig. 2.51. Base of the right first metacarpal bone. A. Anterior aspect. B. Lateral aspect. C. Medial aspect

The bases of the second and third, third and fourth, and fourth and fifth metacarpal bones also articulate with each other. The base of each of the metacarpal bones has certain characteristics that enable us to distinguish them from each other as described below.

Some Features of Individual Metacarpal Bones The base of the first metacarpal bone (Fig. 2.51) bears a large articular surface on its proximal aspect for articulation with the trapezium. This articular surface is saddle shaped being convex from side to side and concave from front to back. The medial and lateral sides of the base are non-articular. The bone is shorter and thicker than any other metacarpal bone. In the intact hand the first metacarpal is unique in that it is widely separated from the other metacarpal bones; it is much more mobile; and it appears to have been rotated through ninety degrees so that its palmar surface faces medially (and not forwards), and the dorsal surface faces laterally (and not backwards). The palmar surface of the shaft is subdivided by a ridge into a larger lateral part and a smaller medial part.

Fig. 2.52. Base of the right second metacarpal bone.A. Anterior aspect. B. Inferior aspect. C. Medial aspect. D. Lateral aspect.

The second metacarpal bone (Fig. 2.52) has a grooved base which articulates with the trapezoid bone. The groove is bounded, medially, by a prominent ridge which articulates with the capitate bone. The base also articulates, laterally,

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with the trapezium and, medially, with the base of the third metacarpal bone. The third metacarpal bone (Fig. 2.53) is distinguished by the presence of a styloid process which is attached to the lateral and dorsal part of the base. The proximal aspect of the base articulates with the capitate bone. The base also articulates with the second metacarpal, laterally, and with the fourth metacarpal, medially.

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Fig. 2.54. Base of right fourth metacarpal. A. Anterior aspect. B. Medial aspect. C. Lateral aspect.

The base of the fourth metacarpal bone (Fig. 2.54) articulates proximally with the hamate bone. The medial side of the base articulates with the fifth metacarpal bone by a single facet. Laterally, the base articulates with the third metacarpal by two discrete facets. The base of the fifth metacarpal bone (Fig. 2.55) articulates proximally with the hamate bone. Its lateral side articulates with the fourth metacarpal, but the medial side is nonarticular.

Fig. 2.53. Base of right third metacarpal bone. A. Anterior aspect. B. Lateral aspect. C. Medial

The fourth and fifth metacarpal bones can be distinguished from each other by examining the medial and lateral sides of their bases. As stated above the fifth

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metacarpal has a facet only on one (lateral) side, while the fourth metacarpal has facets on both the lateral and medial sides of its base.

Determination of the side to which a Metacarpal Bone belongs The proximal and distal ends of any metacarpal bone can be easily differentiated as the head of the bone is placed distally. The palmar and dorsal aspects are also easily recognized as the shaft is concave on the palmar aspect and convex dorsally. It follows that the side to which a metacarpal bone belongs can be determined if we can distinguish between the medial and lateral sides of the bone. This can be done as follows. 1. F irst metacarpal: The palmar surface of the shaft is divided into a larger lateral part and a smaller medial part. Fig. 2.55. Base of right fifth metacarpal bone. A. Lateral aspect. B. Anterior aspect. C. Medial aspect.

2. Second metacarpal: The ridge on the base is medial to the groove. 3. Third metacarpal: The styloid process is attached to the lateral part of the base. 4. Fourth metacarpal: There are two facets on the lateral side of the base, and only one on the medial side. 5. Fifth metacarpal: The medial side of the base is non- articular; but the lateral side has a facet for the fourth metacarpal. For distinction between metacarpal and metatarsal bones see Chapter 3.

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THE PHALANGES OF THE HAND Each digit of the hand, except the thumb, has three phalanges: proximal, middle and distal (Fig. 2.38). The thumb has only two phalanges, proximal and distal. Each phalanx has a distal end or head, a proximal end or base, and an intervening shaft or body.

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The base of each proximal phalanx is concave for articulation with the rounded head of the corresponding metacarpal bone. Its head is pulley shaped. The base of the middle phalanx bears two small concave facets (separated by a ridge) to fit the two convexities on the head of the proximal phalanx. Its distal end is pulley shaped like that of the proximal phalanx. The proximal end of the distal phalanx is similar to that of the middle phalanx. Its distal end is non-articular and irregular in shape.

Attachments on the Skeleton of the Hand A large number of muscles are attached to the bones of the hand (Figs. 2.57, 2.58). Understanding is facilitated by considering separately, the muscles that are intrinsic to the hand; and those which are located in the forearm, but have tendons that gain insertion into bones of the hand. It will be obvious that in the case of the former group both the origins and insertions will be seen, while in the case of the latter group, only the insertions will be encountered in the hand.

Fig. 2.56. The phalanges of a typical digit of the hand

A. Muscles of the front of the forearm that gain insertion into bones of the hand. 1. The flexor carpi radialis is inserted into the palmar surface of the bases of the 2nd and 3rd metacarpal bones. 2. The flexor carpi ulnaris is inserted into the proximal part of the pisiform bone. 3. The flexor digitorum superficialis is inserted on both sides of the middle phalanges of all digits except the thumb. 4. The flexor digitorum profundus is inserted on the bases of the distal phalanges of all digits except the thumb.

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Fig. 2.57. Skeleton of the right hand showing attachments on the palmar aspect. O = Origin. I = Insertion.

5. The flexor pollicis longus is inserted into the palmar surface of the base of the distal phalanx of the thumb.

B. Muscles on the back of the forearm that gain insertion into bones of the hand (Fig. 2.58) 1. The extensor carpi ulnaris is inserted into the medial side of the base of the fifth metacarpal bone. 2. The extensor carpi radialis brevis is inserted into the dorsal aspect of the bases of the 2nd and 3rd metacarpal bones. 3. The extensor carpi radialis longus is inserted into the dorsal aspect of the base of the 2nd metacarpal bone.

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Fig. 2.58. Skeleton of the right hand showing attachments on the dorsal aspect.

4. The abductor pollicis longus is inserted into the lateral side of the base of the first metacarpal bone. 5. The extensor pollicis brevis is inserted on the dorsal aspect of the base of the proximal phalanx of the thumb. 6. The extensor pollicis longus is inserted on the base of the distal phalanx of the thumb. 7. The extensor digitorum is inserted into the bases of middle phalanges, and of distal phalanges, of all digits except the thumb.

C. Attachments of the thenar muscles (Fig. 2.57) 1. The abductor pollicis brevis arises from the tubercle of the scaphoid and from the proximal part of the tubercle of the trapezium. It is inserted on the lateral side of the base of the proximal phalanx of the thumb.

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2. The opponens pollicis arises from the middle of the tubercle of the trapezium. It is inserted into the lateral part of the palmar surface of the shaft of the first metacarpal bone. 3. The flexor pollicis brevis has two heads. The superficial head arises from the distal part of the tubercle of the trapezium; and the deep head from the trapezoid and capitate bones. It is inserted into the lateral side of the base of the proximal phalanx of the thumb. 4. The adductor pollicis has two heads. The oblique head arises from the bases of the 2nd and 3rd metacarpal bones, and from the capitate. The transverse head arises from the distal two thirds of the ridge separating the medial and lateral surfaces of the third metacarpal bone. The muscle is inserted into the medial side of the base of the proximal phalanx of the thumb.

D. Attachments of the hypothenar muscles. 1. The flexor digiti minimi arises from the hook of the hamate. It is inserted into the medial side of the base of the proximal phalanx of the little finger (along with the abductor digiti minimi). 2. The abductor digiti minimi arises from the medial and distal part of the pisiform bone. It is inserted into the medial side of the base of the proximal phalanx of the little finger (along with the flexor digiti minimi). 3. The opponens digiti minimi arises from the hook of the hamate; and is inserted into the medial surface of the 5th metacarpal bone.

E. Attachments of interossei (Figs. 2.59, 2.60) There are four palmar and four dorsal interossei. Each palmar interosseous muscle takes origin from one metacarpal bone; and each dorsal interosseous muscle from adjacent sides of two metacarpal bones. 1. The first palmar interosseous muscle takes origin from the medial side of the base of the first metacarpal bone. 2. The second palmar interosseous muscle takes origin from the medial surface of the palmar aspect of the shaft of the 2nd metacarpal bone. 3. The third palmar interosseous muscle arises from the lateral surface of the palmar aspect of the shaft of the 4th metacarpal bone. 4. The fourth palmar interosseous muscle arises from the lateral surface of the palmar aspect of the shaft of the 5th metacarpal bone.

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Fig. 2.59. Attachments of palmar interossei. Note insertions into dorsal digital expansions.

Fig. 2.60. Attachments of dorsal interossei of the hand. Note insertions into dorsal digital expansions.

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5. The first dorsal interosseous muscle arises from the dorsal aspect of the contiguous sides of the shafts of the 1st and 2nd metacarpal bones. 6. The second dorsal interosseous muscle arises similarly from the contiguous sides of the shafts of the 2nd and 3rd metacarpals. 7. The third dorsal interosseous muscle arises similarly from the contiguous sides of the shafts of the 3rd and 4th metacarpal bones. 8. The fourth dorsal interosseous muscle arises similarly from the contiguous sides of the shafts of the 4th and 5th metacarpal bones. All the interossei are inserted mainly into dorsal digital expansions. Each dorsal interosseous muscle also gains insertion into the base of one proximal phalanx.

F. Other attachments on bones of the hand. 1. The capsular ligament of the wrist joint is attached along the margins of the articular surface formed by the scaphoid, lunate and triquetral bones. 2. The capsules of the various intercarpal, carpometacarpal, metacarpophalangeal and interphalangeal joints are attached around the corresponding articular surfaces. 3. The pisometacarpal ligament is attached to the distal aspect of the pisiform bone, and to the anterior aspect of the base of the fifth metacarpal bone. The pisohamate ligament connects the pisiform bone to the hook of the hamate. These two ligaments transmit the pull of the flexor carpi ulnaris to the fifth metacarpal and hamate bones. 4. The flexor retinaculum is attached medially to the pisiform bone and to the hook of the hamate. Laterally it is attached to the tubercle of the scaphoid and to the tubercle of the trapezium. 5. The medial end of the extensor retinaculum is attached to the triquetral and pisiform bones. 6. On the palmar aspect of each phalanx, the lateral margins give attachment to the fibres of the fibrous flexor sheaths. 7. The dorsal aspect of the phalanges are covered by the dorsal digital expansions.

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Ossification of the Bones of the Hand 1. Each carpal bone is ossified from one centre that (as a rule) appears as follows: Capitate:

2nd month

Hamate:

3rd month

Triquetral:

3rd year

Lunate:

4th year

Scaphoid:

4th to 5th year

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Trapezium: 4th to 5th year Trapezoid:

4th to 5th year

Pisiform:

About 10th year

2. Each metacarpal has a primary centre for the shaft that appears in the 9th fetal week. The first metacarpal has a secondary centre for the base that appears in the 2nd or 3rd year, and unites with the shaft at about 16 years. The other metacarpal bones have secondary centres (not in the base but) in the heads. These appear at about 2 years of age and unite with the shaft between 16 and 18 years of age. 3. Each phalanx has a primary centre for the shaft and a secondary centre for its proximal end. The primary centre appears first in the distal phalanges (about the 8th week); next in the proximal phalanges (about the 10th week); and last in the middle phalanges (about the 12th fetal week). The secondary centres appear first in the proximal phalanges (2nd year) and later in the middle and distal phalanges (3rd or 4th year). They unite with the shafts between 16 to 18 years of age.

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3 Bones of the Lower Limb

A brief introduction to the bones of the lower limb has been given in Chapter 1. We will now consider each bone one by one.

The Hip Bone Introductory remarks The hip bone (Figs. 3.2, 3.3) constitutes the pelvic girdle. Along with the sacrum and coccyx, the right and left hip bones form the bony pelvis (Fig. 3.1). The orientation of the hip bone in the body is best appreciated by viewing it in the intact pelvis. Each hip bone consists of three parts. These are the ilium, the pubis, and the ischium. These three parts meet at the acetabulum which is a large deep cavity placed on the lateral aspect of the bone. The acetabulum takes part in forming the hip joint along with the head of the femur. Below and medial to the acetabulum the hip bone shows a large oval or triangular aperture called the obturator foramen. The ilium consists, in greater part, of a large plate of bone which lies above and behind the acetabulum, and forms the side wall of the greater pelvis. Its upper border is in form of a broad ridge that is convex upwards: this ridge is called the iliac crest. The posterior part of the ilium bears a large rough articular area on its medial side for articulation with the sacrum. The pubis lies in relation to the upper and medial part of the obturator foramen. It forms the most anterior part of the hip bone. The two pubic bones meet in the middle line, in front, to form the pubic symphysis. The lowest part of the hip bone is formed by the ischium which lies below and behind the acetabulum and the obturator foramen. Using the information given above, a given hip bone can be correctly orientated and its side determined.

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Fig. 3.1. Pelvis viewed from the front. The sacrum is shown only in its left half, and the femur only on the right side.

We will now consider the features of the ilium, the ischium and the pubis in detail. Features seen on the lateral aspect are shown in figure 3.2 and those seen on the medial aspect are shown in figure 3.3.

The Ilium In addition to the features already mentioned note the following. The anterior end of the iliac crest projects forwards as the anterior superior iliac spine. The posterior end of the crest also forms a projection called the posterior superior iliac spine. The iliac crest may be subdivided into a ventral segment, consisting of the anterior two-thirds of the crest, and a dorsal segment consisting of the posterior one third. The whole length of the ventral segment shows a broad intermediate area which is bounded by inner and outer lips (Fig. 3.4A). The outer lip of the iliac crest is most prominent about 5 cm behind the anterior superior iliac spine. This prominence is called the tubercle of the iliac crest. The dorsal segment of the iliac crest has medial and lateral surfaces separated by a ridge (Fig. 3.4B). The anterior border of the ilium extends from the anterior superior iliac spine to the acetabulum. Its lowest part presents a prominence called the anterior inferior iliac spine.

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Fig. 3.2. Right hip bone, external aspect.

The posterior border of the ilium extends from the posterior superior iliac spine to the back of the acetabulum. A few centimetres below the posterior superior iliac spine the posterior border presents another prominence called the posterior inferior iliac spine. The lower part of the posterior border forms the upper boundary of a deep notch called the greater sciatic notch. The lateral aspect of the ilium constitutes its gluteal surface. This surface is marked by three ridges called the anterior, posterior and inferior gluteal lines. The posterior gluteal line is vertical. It extends from the iliac crest, above, to the posterior inferior iliac spine below.

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Fig. 3.3. Right hip bone, internal aspect.

The anterior gluteal line is convex upwards and backwards. Its anterior end meets the iliac crest in front of the tubercle; while its posterior end reaches the greater sciatic notch. The inferior gluteal line is horizontal. Its anterior end lies just above the anterior inferior iliac spine; and its posterior end reaches the greater sciatic notch. The gluteal surface of the ilium bears a prominent groove just above the acetabulum. The lower part of the gluteal surface extends behind the acetabulum where it becomes continuous with the ischium. The lowest part of the ilium forms the upper two-fifths of the acetabulum. The medial surface of the ilium is divisible into the following parts. The iliac fossa is smooth and concave and forms the wall of the greater pelvis: it occupies the anterior part of the medial

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Fig. 3.4. Vertical section across the dorsal segment (A), and the ventral segment (B) of the iliac crest. Fig. 3.5. Right ischial tuberosity, seen from behind and below.

surface. The sacropelvic surface lies behind the iliac fossa. It can be subdivided into three parts. The upper part is rough and constitutes the iliac tuberosity. The middle part articulates with the lateral side of the sacrum. This part is called the auricular surface because of a resemblance to the pinna. The pelvic part of the medial surface lies below and in front of the auricular surface. It is smooth and takes part in forming the wall of the lesser pelvis. This surface is often marked (specially in the female) by a rough groove called the preauricular sulcus. The iliac fossa and the sacropelvic surface are separated by the medial border of the ilium. This border is sharp in its upper part where it separates the iliac fossa from the auricular surface. Its lower part is rounded and forms the arcuate line. The lower end of the arcuate line reaches the junction of the ilium and pubis. This junction shows an enlargement called the iliopubic eminence.

Fig. 3.6. Medial part of right hip bone: anterosuperior aspect.

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The Ischium The ischium consists of a main part called the body, and a projection called the ramus. The upper end of the body forms the inferior and posterior part of the acetabulum. The lower part of the body has three surfaces: dorsal, femoral and pelvic. The lower part of the dorsal surface has 3 a large rough impression called the ischial tuberosity. This tuberosity is divided into upper and lower parts by a transverse ridge (Fig. 3.5). Each of these parts is again divided into medial and lateral parts.The part of the dorsal surface above the ischial tuberosity shows a wide shallow groove. Superiorly, the dorsal surface of the ischium becomes continuous with the gluteal surface of the ilium. The posterior border of the dorsal surface of the ischium forms part of the lower margin of the greater sciatic notch. Just below this notch the border projects backwards and medially as the ischial spine. Between the ischial spine and the upper border of the ischial tuberosity we see a shallow lesser sciatic notch. The femoral surface of the ischium is directed downwards, forwards and laterally. It is continuous with the external surface of the ramus of the ischium which is attached to the medial side of the lower end of the body. The ramus has an anterior (external) surface and a posterior (internal) surface.

The Pubis The pubis consists of a body, a superior ramus and an inferior ramus. The body (Fig. 3.6) forms the anterior and most medial part of the hip bone. It has an anterior surface and a posterior surface. The upper border of the body forms a prominent ridge called the pubic crest. The crest ends laterally in a projection called the pubic tubercle. The superior ramus of the pubis is attached to the upper and lateral part of the body. It runs upwards backwards and laterally. Its lateral extremity takes part in forming the pubic part of the acetabulum. It meets the ilium at the iliopubic eminence. The superior ramus is triangular in cross section (Fig. 3.7). It has three borders and three surfaces. The anterior border is called the obturator crest. The posterior border is sharp and forms the pecten pubis or pectineal line. The inferior border is also sharp and forms the upper margin of the obturator foramen. The surface between the obturator crest and the pecten pubis is the pectineal surface. The pelvic surface lies between the pecten pubis and the inferior border. The surface between the obturator crest and the inferior border is called the obturator surface. A groove runs forwards and downwards across it and is called the obturator groove. The inferior ramus is attached to the lower and lateral part of the body of the pubis. It passes downwards and laterally to meet the ramus of the ischium. These two rami form the medial boundary of the obturator foramen.

Fig. 3.7. Section at right angles to the long axis of the superior ramus of the pubis.

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In the intact pelvis (Fig. 3.1) the conjoined rami of the pubis and ischium of the two sides form the boundaries of the pubic arch which lies below the pubic symphysis. The inferior ramus of the pubis has an anterior (or outer) surface, and a posterior (or inner) surface. These surfaces are continuous with corresponding surfaces of the ischial ramus.

The Acetabulum The acetabulum is a deep cup like cavity that lies on the lateral aspect of the hip bone. It forms the hip joint with the head of the femur. It is directed laterally and somewhat downwards and forwards. The margin of the acetabulum is deficient in the anteroinferior part: the gap in the margin is called the acetabular notch. The floor of the acetabulum is partly articular and partly non-articular. The articular area for the head of the femur is shaped like a horse-shoe and is called the lunate surface. This surface is widest superiorly. The inner border of the lunate surface forms the margin of the non-articular part of the floor which is called the acetabular fossa. The contributions to the acetabulum by the ilium, the ischium and the pubis are shown in figures 3.6 and 3.9.

The Obturator Foramen The obturator foramen is bounded above by the superior ramus of the pubis; medially by the body of the pubis, by its inferior ramus and by the ramus of the ischium; and laterally by the body of the ischium. In the intact body the foramen is filled by a fibrous sheet called the obturator membrane. However the membrane is deficient in the uppermost part of the foramen: here the membrane has a free upper edge which is separated from the superior ramus of the pubis by a gap.

Attachments on the Hip Bone A. The muscles attached to the iliac crest are as follows (Figs. 3.8, 3.9) 1. The internal oblique muscle of the abdomen arises from the intermediate area of the ventral segment of the iliac crest. 2. The external oblique muscle of the abdomen is inserted into the anterior two thirds of the outer lip of the ventral segment of the iliac crest. 3. The lowest fibres of the latissimus dorsi take origin from the outer lip of the iliac crest just behind its highest point. 4. The tensor fasciae latae arises from the anterior part of the outer lip of the iliac crest. 5. The transversus abdominis arises from the anterior two-thirds of the inner lip of the ventral segment of the iliac crest.

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3

Fig. 3.8. Right hip bone, showing attachments. External aspect.

6. The quadratus lumborum arises from the posterior one third of the inner lip of the ventral segment of the iliac crest. 7. The gluteus maximus arises from the lateral surface of the dorsal segment of the iliac crest and from the gluteal surface of the ilium behind the posterior gluteal line. 8. The erector spinae arises from the medial surface of the dorsal segment of the iliac crest.

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B. The muscles attached to the external aspect of the hip bone (excluding the iliac crest) are as follows (Fig. 3.8) 1. See origin of gluteus maximus described above. 2. The gluteus medius arises from the gluteal surface of the ilium between the anterior and posterior gluteal lines. 3. The gluteus minimus arises from the gluteal surface of the ilium between the anterior and inferior gluteal lines. 4. The sartorius arises from the anterior superior iliac spine and from a small area below the spine. 5. The straight head of the rectus femoris arises from the anterior inferior iliac spine; and its reflected head from the groove above the acetabulum. 6. A few fibres of the piriformis arise from the upper border of the greater sciatic notch near the posterior inferior iliac spine. 7. The pectineus arises from the upper part of the pectineal surface of the superior ramus of the pubis. 8. The rectus abdominis (lateral head) arises from the pubic crest. 9,10. The pyramidalis and the adductor longus arise from the anterior surface of the body of the pubis. 11. The gracilis arises from the anterior surface of the body, and the inferior ramus, of the pubis; and from the ramus of the ischium. 12. The adductor brevis arises from the anterior surface of the body of the pubis and its inferior ramus, lateral to the origin of the gracilis. 13. The obturator externus arises from the superior and inferior rami of the pubis, and from the ramus of the ischium, immediately around the obturator foramen. 14. The adductor magnus arises from the lower lateral part of the ischial tuberosity, and from the ramus of the ischium. 15,16. The semitendinosus and the biceps femoris (long head) arise from the upper medial part of the ischial tuberosity. 17. The semimembranosus arises from the upper lateral part of the ischial tuberosity. 18. The quadratus femoris arises from the femoral surface of the ischium just lateral to the ischial tuberosity.

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Fig. 3.9. Right hip bone, showing attachments. Internal aspect.

19. The superior gemellus arises from the dorsal surface of the ischial spine. 20. The inferior gemellus arises from the ischium just above the ischial tuberosity.

C. The muscles arising from the internal aspect of the hip bone are as follows (Fig. 3.9) 1. The iliacus arises from the upper two thirds of the iliac fossa.

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2. The obturator internus arises from the pelvic surfaces of the superior and inferior rami of the pubis, and the ramus of the ischium, immediately adjoining the obturator foramen; and from the pelvic surfaces of the ischium and of the ilium. 3. The most posterior fibres of the levator ani arise from the pelvic surface of the ischial spine; and its most anterior fibres from the posterior surface of the body of the pubis. 4. The psoas minor is inserted into the pecten pubis and into the iliopectineal eminence. 5. The coccygeus arises from the pelvic surface of the ischial spine. 6. The superficial transversus perinei and the ischiocavernosus arise from the posterior surface of the ramus of the ischium. 7. The sphincter urethrae arises from the posterior surfaces of the inferior pubic and ischial rami.

D. Other attachments on the Hip Bone 1. The inguinal ligament is attached medially to the pubic tubercle, and laterally to the anterior superior iliac spine. 2. The apex of the lacunar ligament is attached to the pubic tubercle; and its posterior edge to the medial part of the pecten pubis. 3. The conjoint tendon is attached to the pubic crest and to the medial part of the pecten pubis. 4. The margin of the acetabulum gives attachment to the capsule of the hip joint, and to the acetabular labrum. The capsule of the sacroiliac joint is attached around the margin of the auricular surface. 5. The deep fascia of the thigh (fascia lata) is attached to the outer lip of the iliac crest. The fascia attached to the anterior part of the crest is thick and forms the iliotibial tract. The fascia is also attached to the lower border of the ischiopubic rami. 6. The conjoined ischiopubic rami give attachment to the superior and inferior fasciae of the urogenital diaphragm. 7. The dorsal and interosseous sacroiliac ligaments are attached to the iliac tuberosity. 8. The upper end of the sacrotuberous ligament is attached to the posterior superior and posterior inferior iliac spines, and to the intervening part of the posterior border of the ilium. The lower end of the ligament is attached to the medial margin of the ischial tuberosity. The attachment of the ligament extends on to the ramus of the ischium as a thin band called the falciform process. 9. The sacrospinous ligament is attached to the apex of the ischial spine.

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Important Relations of Hip Bone 1. The posterior surface of the pubis is related to the urinary bladder. 2. The right iliac fossa is related to the caecum and terminal ileum. The left iliac fossa is 3 related to the terminal part of the descending colon. 3. The greater and lesser sciatic notches are converted into foramina by the sacrotuberous and sacrospinous ligaments. The greater sciatic foramen transmits the following structures: Piriformis; the superior and inferior gluteal nerves and vessels; the internal pudendal vessels; the pudendal and sciatic nerves; the posterior cutaneous nerve of the thigh; and the nerves to the obturator internus and to the quadratus femoris. Having emerged from the greater sciatic foramen the pudendal nerve, the nerve to the obturator internus, and the internal pudendal vessels pass behind the ischial spine to enter the lesser sciatic foramen. The tendon of the obturator internus emerges from the pelvis through this foramen. Ossification of the Hip Bone The hip bone has three primary centres, one each for the ilium, the ischium and the pubis. The centres appear in intrauterine life as follows: for the ilium in the 8th week; for the ischium in the fourth month; and for the pubis in the fourth or fifth month. At birth the ilium, ischium and pubis are separated by a Y- shaped cartilage present in the region of the acetabulum. The three parts fuse completely only after the age of 18 years. The inferior ramus of the pubis and the ramus of the ischium are at first separated by cartilage. They fuse with each other about the seventh year. Several secondary centres appear in the hip bone. There are two in the iliac crest, two in the acetabular cartilage, and occasional centres in the anterior inferior iliac spine, the lower part of the acetabulum, the pubic tubercle and the pubic crest. These centres appear at about the age of puberty or later and fuse with the rest of the bone between 20 and 25 years of age.

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Pelvis as a whole We have seen that the bony pelvis is made up of the two hip bones, the sacrum and the coccyx (Fig. 3.10). (Note: References made to the sacrum and coccyx will be clear after these bones have been studied. They are described in Chapter 4). It may be subdivided into the greater (or false) pelvis and the lesser (or true) pelvis. The walls of the greater pelvis are formed by the broad upper parts of the two iliac bones (iliac fossae), and posteriorly by the base of the sacrum. Note that the greater pelvis has no bony anterior wall, and that it is merely the lower part of the abdomen. The communication between the greater and lesser pelvis is called the superior pelvic aperture or pelvic inlet. The margins of the aperture constitute the pelvic brim. The pelvic brim is formed behind by the sacral promontory, and the ridge separating the superior and anterior surfaces of the sacrum; on either side by the arcuate line of the ilium (also see Fig. 3.3); and anteriorly by the pecten pubis and by the pubic crest. The arcuate line, the pecten pubis and the pubic crest are collectively referred to as the linea terminalis. The cavity of the lesser pelvis is bounded in front by the body and rami of the pubis; on either side by the pelvic surfaces of the ilium and ischium below the arcuate line; and behind by the anterior surfaces of the sacrum and coccyx.

Fig. 3.10. Pelvis seen from the front.

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The inferior pelvic aperture is highly irregular. It is bounded anteriorly by the pubic arch; laterally, in that order, by the ischial tuberosity, the lesser sciatic notch, the ischial spine and the greater sciatic notch. Posteriorly, it is formed by the lateral margin of the sacrum and coccyx. When the ligaments are intact the lateral margins are formed by the sacrotuberous ligaments (that stretch from the side of the sacrum and coccyx to the ischial tuberosity. The inferior 3 aperture then appears to be rhomboidal (Fig. 3.12).

Diameters of the pelvis The diameters of the pelvic inlet and outlet are important in obstetrics. Some of these are as follows. All dimensions given are those in the female.

A. INLET (Fig. 3.11) (a) The anteroposterior diameter is measured from the upper border of the symphysis pubis to the sacral promontory. It is about 110 mm in the female. (b) The transverse diameter is measured across the widest part of the pelvic brim. It is about 130 mm. (c) The oblique diameter is measured from one iliopubic eminence to the opposite sacroiliac joint. It is about 125 mm.

Fig. 3.11. Anteroposterior view of the pelvis to show the diameters of the pelvic inlet (in mm).

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B. OUTLET (Fig. 3.12) (a) The anteroposterior diameter is measured from the apex of the coccyx to the lower border of the symphysis pubis. It is about 125 mm. (b) The transverse diameter is measured between the two ischial tuberosities. It is about 110 mm. (c) The oblique diameter is measured from the midpoint of the sacrotuberous ligament of one side to the junction of the ischial and pubic rami on the other side. It is about 118 mm. It is important to know the exact orientation of the pelvis in the body. The pelvis is so placed that the anterior Fig. 3.12. Pelvic outlet seen from below. superior iliac spines and the top of the pubic symphysis are in the same vertical plane. (The pelvis can be so held by placing it against any vertical surface with the points mentioned above touching it.) When the pelvis is orientated in this way the pelvic inlet faces forwards and upwards, its plane being at an angle of 50 to 60 degrees with the horizontal plane (Fig. 3.13). The pelvic outlet faces downwards and slightly backwards, making an angle of about 15 degrees with the horizontal plane. The axis of the pelvic passage is a curved one corresponding to the curve of the sacrum.

Sex Differences in the Pelvis Of all the bones of the human skeleton sexual differences are most marked in the pelvis, and these are useful in deciding whether a given pelvis belongs to a male or a female individual. Some of these differences are of a general nature and are not very useful in determining the sex of a particular specimen. As a rule, the male pelvis is more strongly built than in the female, and the bones have more prominent muscular markings. All the articular areas including the acetabulum are larger in the male, for transmission of greater body weight. In contrast the female pelvis is adapted for the function Fig. 3.13. Schematic sagittal section of the pelvis to show orientation of the pelvic inlet and outlet.

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Fig. 3.15. Shape of the greater sciatic notch in the male and female.

Fig. 3.14. Anteroinferior aspect of the pelvis(A) in the male, and (B) in the female.

of child bearing. For this purpose the true pelvis is broader and shallower than in the male. The points that are really useful in deciding the sex of a given pelvis are as follows.

Fig. 3.16. Comparison of the relative size of the articular surface on the sacrum for the body of the fifth lumbar vertebra, in the male and female.

However, all the features have to be taken together, no one feature being decisive. (1) The subpubic angle (i.e. the angle between the right and left ischiopubic rami) is almost ninety degrees in the female, but is only fifty to sixty degrees in the male (‘a’ in Figs. 3.14 A,B). The angle is sharp in the male, but tends to be rounded in the female. (2) The medial edges of the ischiopubic rami may be markedly everted in the male (‘b’ in Fig. 3.15A) for attachment of the crura of the penis. (3) In Figs. 3.14 A and B lines xy represent the distance from the pubic symphysis to the anterior margin of the acetabulum. Lines yz represent the total width of the acetabulum. In the male (Fig. 3.14A) xy = yz; but in the female (Fig. 3.14B) xy is distinctly more than yz. (4) The pubis, the ischium and the ilium meet at a point in the floor of the acetabulum (‘m’ in Figs. 3.14A,B). Line mn represents the height of the ischium, and xm is the length of the pubis. The value xm / mn x 100 is less than ninety in the male and more than ninety in the female. This is called the puboischial index (of Washburn).

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(5) Because of the greater width of the pubis in the female the obturator foramen tends to be triangular (Fig. 3.14B). In the male it tends to be ovoid (Fig. 3.14A). (6) The greater sciatic notch (Fig. 3.15) is wide (and deep) in the typical female pelvis. It is narrow in the typical male pelvis. However, because of considerable variability in shape this is not a very useful feature in sexing the pelvis. (7) In the female sacrum the width of the articular area for the body of the fifth lumbar vertebra is equal to the width of the lateral part (or ala) (Fig. 3.16). On the other hand, in the male the width of the body is distinctly more than the width of the lateral part.

Fig, 3.17. Shape and relative size of the pelvic inlet in the male and female.

(8) The pelvic inlet is rounded in the female, but tends to be heart shaped in the male. The male inlet is smaller in all diameters (Fig. 3.17). (9) The preauricular sulcus is deeper and more prominent in the female.

The Femur The femur (Figs. 3.18 to 3.24) is a long bone having a shaft, an upper end and a lower end. The upper end is easily distinguished from the lower end by the presence of a rounded head which is joined to the shaft by an elongated neck. The head is directed medially to articulate with the acetabulum of the hip bone. The anterior and posterior aspects of the bone can be distinguished by examining the shaft: it is convex forwards and the anterior aspect is smooth, while the posterior aspect is marked by a prominent vertical ridge called the linea aspera. The information given above is sufficient to distinguish between a femur of the right or left side.

The Upper End Apart from the head and the neck the upper end of the femur has two projections called the greater and lesser trochanters. The head, apart from being directed medially is also directed upwards and somewhat forwards. It is much more rounded than the head of the humerus and is slightly more than half a sphere. Near the centre of the head there is a pit or fovea.

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Fig. 3.19. Right femur: posteromedial view of upper end.

Fig. 3.20. Right femur: lateral aspect of upper end.

Fig. 3.18. Right femur, anterior aspect.

The neck connects the head to the shaft. It joins the shaft at an angle of about 125 degrees. The neck expands as it reaches the shaft. The greater and lesser trochanters are situated near the junction of the neck with the shaft.

The greater trochanter forms a large quadrangular projection on the lateral aspect of the upper end of the femur. Its upper and posterior part projects upwards beyond the level of the neck and thus comes to have a medial surface. On this surface we see a depressed area called the trochanteric fossa (Fig. 3.19). The anterior aspect of the greater trochanter shows a large rough area for muscle attachments. The lateral surface of the greater trochanter is also marked by an area for muscle attachments: the area is in the form of a ridge or a flat strip that runs downwards and forwards across the lateral surface. The lesser trochanter is a conical projection attached to the shaft where the

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lower border of the neck meets the shaft. It points medially and backwards. The posterior parts of the greater and lesser trochanters are joined together by a prominent ridge called the intertrochanteric crest. A little above its middle this crest bears a rounded elevation called the quadrate tubercle. Anteriorly, the junction of the neck and the shaft is marked by a much less prominent intertrochanteric line. The upper end of this line reaches the anterior and upper part of the greater trochanter; its lower end lies a little in front of the lesser trochanter. Here it becomes continuous with the spiral line which runs downwards and backwards across the medial aspect of the shaft to reach its posterior aspect.

The Shaft The shaft of the femur has a forward convexity and is smooth anteriorly. Its posterior aspect is marked by a rough vertical ridge called the linea aspera. A section across the shaft is seen in Fig. 3.22. We see that the shaft is triangular having three borders (lateral, medial and posterior) and three surfaces (anterior, lateral and medial). The lateral and medial borders are rounded. The posterior border corresponds

Fig. 3.21. Right femur, posterior aspect. Fig. 3.22. TS across the shaft of the femur near its middle.

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to the linea aspera. It will be seen from figure 3.22 that in addition to the directions indicated by their names the medial and lateral surfaces also face backwards. The linea aspera has distinct medial and lateral lips. When traced upwards to the upper one third of the shaft the lips diverge. The medial lip becomes continuous with the spiral line. The lateral lip of the linea aspera becomes continuous with a broad rough area called the gluteal tuberosity. The upper end of 3 the gluteal tuberosity reaches the greater trochanter. The area between the gluteal tuberosity (laterally) and the spiral line (medially) constitutes a fourth surface (posterior) over the upper one third of the shaft. The two lips of the linea aspera also diverge from each other over the lower one third of the shaft to become continuous with ridges called the medial and lateral supracondylar lines. Here again, the shaft has an additional surface directed posteriorly: this surface is triangular and is called the popliteal surface.

The Lower End The lower end of the femur consists of two large condyles — medial and lateral. The two condyles are joined together anteriorly and, on this aspect, they lie in the same plane as the lower part of the shaft (Fig. 3.23). Posteriorly, the two condyles project much beyond the plane of the shaft, and here they are separated by a deep intercondylar notch or fossa.

Fig. 3.23. Right femur, lower end, viewed from below.

Fig. 3.24. Right femur, lower end, seen from the lateral side.

When viewed from the side (Fig. 3.24) the lower margin of each condyle is seen to form an arch that is convex downwards. When seen from below (Fig. 3.23) it is seen that the long axis of the lateral condyle is straight and is directed backwards and somewhat laterally. (In Fig. 3.23 the axis is indicated in interrupted line). In contrast the medial condyle is slightly curved having a medial convexity. The anterior aspect of the two condyles is marked by an articular area for the patella (Fig. 3.23). The area is concave from side to side to accommodate the convex posterior surface of the patella. It is divided into medial and lateral parts. The lateral part is much larger. (Also see Fig. 3.18). Inferiorly, the condyles articulate with the tibia to form the knee joint. For this purpose each condyle bears a large convex articular surface which is continuous anteriorly with the patellar surface. The articular surface covers the inferior and posterior aspects of each condyle.

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When seen from the lateral aspect the lateral condyle of the femur is seen to be more or less flat (Fig. 3.24). A little behind the middle it is marked by a prominence called the lateral epicondyle. Behind and below the epicondyle there is a prominent groove that is divided into an anterior deeper part and a shallower posterior part. When seen from the medial aspect the medial condyle is seen to be convex. The most prominent point on it is called the medial epicondyle (Fig. 3.23). The uppermost part of the medial condyle is marked by a prominence called the adductor tubercle (Fig. 3.21). This tubercle lies above and behind the medial epicondyle and is continuous with the lower end of the medial supracondylar line.

Attachments on the Femur A. The muscles inserted into the femur are as follows (Figs. 3.25, 3.26) 1. The gluteus minimus is inserted on the anterior aspect of the greater trochanter. 2. The gluteus medius is inserted into the oblique strip running downwards and forwards across the lateral surface of the greater trochanter. 3. The piriformis is inserted into the upper border of the greater trochanter. 4. The obturator internus and gemelli are inserted into the anterior part of the medial surface of the greater trochanter. 5. The obturator externus is inserted into the trochanteric fossa on the medial surface of the greater trochanter. 6. The psoas major is inserted into the medial part of the anterior surface of the lesser trochanter. 7. The iliacus is inserted into the medial side of the base of the lesser trochanter, and into a small area below the latter. 8. The pectineus is inserted along a line descending from the root of the lesser trochanter to the upper end of the linea aspera. The insertion lies between the gluteal tuberosity and the spiral line. 9. The quadratus femoris is inserted on the quadrate tubercle, and into a small area below the latter. 10. The deep fibres of the gluteus maximus are inserted into the gluteal tuberosity. 11. The upper part of the adductor brevis is inserted between the insertions of the pectineus (medially) and the adductor magnus (laterally) (see below). The lower part of the muscle is inserted into the linea aspera.

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Fig. 3.25. Right femur, showing attachments, seen from the front.

Fig. 3.26. Right femur, showing attachments, seen from behind.

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12. The adductor longus is inserted into the middle one third of the linea aspera. 13. The adductor magnus is inserted into the medial margin of the gluteal tuberosity, the linea aspera, and the medial supracondylar line. The hamstring part of the muscle ends in a tendon which is attached to the adductor tubercle.

B. The muscles taking origin from the femur are as follows. 1. The vastus lateralis has a long linear origin. The line begins at the upper end of the intertrochanteric line, and passes along the anterior and lower borders of the greater trochanter, the lateral margin of the gluteal tuberosity, and the lateral lip of the linea aspera. 2. The vastus medialis also has a long linear origin from the lower part of the intertrochanteric line, the spiral line, the medial lip of the linea aspera, and the medial supracondylar line right up to the adductor tubercle. 3. The vastus intermedius arises from the upper three fourths of the anterior and lateral surfaces of the shaft. The medial surface of the shaft does not give origin to the muscle, but is covered by it. 4. The articularis genu arises from small areas on the anterior surface of the shaft below the origin of the vastus intermedius. 5. The short head of the biceps femoris arises from the linea aspera and from the upper part of the lateral supracondylar line. 6. The medial head of the gastrocnemius arises from the popliteal surface a little above the medial condyle. The lateral head of the muscle arises from the lateral surface of the lateral condyle. 7. The plantaris arises from the lower part of the lateral supracondylar line. 8. The popliteus arises (by a tendon) from the anterior part of the groove on the lateral aspect of the lateral condyle.

C. Other attachments on the femur. 1. The capsular ligament of the hip joint is attached to the neck of the femur most of which is intracapsular. Anteriorly, the capsule is attached to the intertrochanteric line, but posteriorly the capsule is attached about 1 cm medial to the intertrochanteric crest. 2. The ligament of the head is attached to the fovea on the head of the femur.

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3. The capsular ligament of the knee joint is attached to the femoral condyles and to the posterior margin of the intercondylar fossa. On the lateral condyle it is attached above the origin of the popliteus. The capsule is deficient anteriorly, where it is replaced by the patella. 4. The anterior cruciate ligament is attached to the medial surface of the lateral condyle.

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5. The posterior cruciate ligament is attached to the lateral surface of the medial condyle.

Ossification of the Femur 1.

The femur is the second long bone in the body to start ossifying (the first being the clavicle). The primary centre appears in the shaft during the 7th fetal week. It may be noted that the neck of the femur ossifies from the primary centre.

2.

Three secondary centres appear at the upper end of the bone, one each for the head (first year), the greater trochanter (4th year), and the lesser trochanter (around the 12th year). Each centre fuses independently with the shaft in the reverse order of appearance: the lesser trochanter at about 13 years, the greater trochanter at about 14 years, and the head around 16 years.

3. One centre appears for the distal end. This centre appears before birth in the 9th month of fetal life. It fuses with the shaft between the 16th and 18th years.

The Patella The tendons of some muscles have, embedded in them, small bones that help them to glide over bony surfaces. Such bones are called sesamoid bones. The largest sesamoid bone in the body is to be seen in the tendon of the quadriceps femoris as it passes in front of the knee joint. It is called the patella. The patella is shaped somewhat like a disc (Figs. 3.27, 3.28). It roughly triangular in outline. It has anterior and posterior surfaces that are separated by three borders: superior, medial, and lateral. The superior border is also called the base. The inferior part of the bone shows a downward projection representing the apex of the triangle. The anterior surface is rough and can be felt through the overlying skin. The upper part of the posterior surface is articular. This part articulates with the patellar surface on the anterior aspect of the condyles of the femur. It consists of a larger lateral part and a smaller medial part, the two parts being separated by a ridge. The most medial part of the articular area may be

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Fig. 3.27. Right patella, anterior aspect.

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Fig. 3.28. Right patella, posterior aspect.

recognizable as a separate area: this part articulates with the medial condyle of the femur only in extreme flexion of the knee joint. The lower part of the posterior surface is nonarticular. It is rough for attachment of the ligamentum patellae.

Attachments on the Patella 1.

The superior border gives attachment to the rectus femoris and to the vastus intermedius.

2.

The medial margin gives attachment to the medial patellar retinaculum (which is an expansion from the tendon of the vastus medialis).

3.

The lateral margin gives attachment to the lateral patellar retinaculum (which is an expansion from the tendon of the vastus lateralis).

4.

The apex gives attachment to the ligamentum patellae.

Ossification of the Patella The patella ossifies from several centres that appear between the third and sixth years of life. The centres soon fuse with one another.

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The Tibia The tibia is the medial bone of the leg. It has a shaft, an upper end and a lower end (Figs. 3.29 to 3.35). The upper end can be distinguished from the lower end as it is much larger. The medial and lateral sides of the bone can be distinguished by examining the lower end: this end has a prominent downward projection, the medial malleolus, on its medial side. The anterior and posterior aspects of the bone can be distinguished by examining the shaft. The shaft is triangular in section (Fig. 3.31) and has a sharp anterior border. The side to which a tibia belongs can be determined from the information given above.

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The Upper End The upper end of the tibia is expanded to form a mass that projects medially, laterally and posteriorly beyond the shaft. When viewed from above (Fig. 3.30) it is seen to consist of two parts called the medial and lateral condyles that are separated by an intercondylar area. The anterior aspect of the upper end of the tibia is marked by another projection called the tibial tuberosity. The upper surfaces of the medial and lateral condyles bear large, slightly concave, articular surfaces that take part in forming the knee joint. The medial articular surface is oval, and is larger than the lateral surface which is rounded. The articular surfaces are separated by the intercondylar area which is nonarticular. The intercondylar area is raised in its central part to form the intercondylar eminence. The medial and lateral parts of the eminence are more prominent than its central part and constitute the medial and lateral

Fig. 3.29. Right tibia, anterior aspect.

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intercondylar tubercles. The medial and lateral condylar articular surfaces extend on to the sides of the intercondylar tubercles. In addition to its upper surface the medial condyle has rough anterior, medial and posterior surfaces that are distinctly marked off from the shaft by a ridge (Figs. 3.30, 3.33). The lateral condyle has similar anterior, lateral and posterior surfaces. The posterior surface of the medial condyle is marked by a groove. The posterolateral part of the lateral condyle bears an oval articular facet for the upper end of the fibula (Figs. 3.32, 3.33). The facet is directed backwards, downwards and laterally. The anterior surfaces of the medial and lateral condyles merge to form a large rough triangular area. The apex of the triangle is placed inferiorly and is raised to form a large projection called the tibial tuberosity. The tuberosity has an upper smooth part and a lower rough part (Fig. 3.29). The lateral margin of the triangle mentioned above has a prominent impression (which is also triangular).

Fig. 3.30. Right tibia, seen from above.

Fig, 3.31. Right tibia. Transverse section through the shaft viewed from below.

The Shaft If we cut a section across the shaft of the tibia (Fig. 3.31) we see that the shaft is triangular. It has anterior, medial and lateral (or interosseous) borders; and medial, lateral and posterior surfaces. The anterior border runs downwards from the tibial tuberosity. Its lower part turns medially and reaches the anterior margin of the medial malleolus. The interosseous or lateral border begins a little below and in front of the articular facet for the fibula. It descends along the lateral aspect of the shaft. Its lower end forms the anterior margin of a rough triangular area seen

Fig. 3.32. Upper end of right tibia. Lateral aspect.

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on the lateral aspect of the lower end (Fig. 3.34). The upper end of the medial border lies below the most medial part of the medial condyle. Its lower end becomes continuous with the posterior margin of the medial malleolus.

3 The medial surface lies between the anterior and medial borders. The upper end of the surface is rough just in front of the medial border. The rest of the surface is smooth and can be felt through the overlying skin. The lateral surface lies between the anterior and interosseous borders. Because of the fact that the anterior border turns medially in its lower part, the lateral surface extends on to the anterior aspect of the lower part of the shaft. The posterior surface (Fig. 3.33) lies between the medial and interosseous borders. Over the upper one-third of the shaft this surface is

Fig. 3.34. Right tibia, lower end, seen from the lateral side.

Fig. 3.33. Right tibia. Posterior aspect

Fig. 3.35. Right tibia, lower end, seen from below.

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marked by a prominent ridge that runs downwards and medially across it. This ridge is called the soleal line. The part of the posterior surface above the soleal line is triangular. The part below the line is subdivided into medial and lateral parts by a faint vertical ridge.

The Lower End The lower end of the tibia is much less expanded than the upper end. Its medial part shows a downward projection called the medial malleolus. The posterior aspect of the malleolus is marked by a prominent groove. The lateral aspect of the lower end (Fig. 3.34) shows a triangular fibular notch for articulation with the fibula. It consists of an upper part which is rough and a lower part which is smooth. The inferior surface of the lower end (Fig. 3.35) bears an articular area that articulates with the upper surface of the talus to form the ankle joint. The area is continuous with another articular area on the lateral aspect of the medial malleolus that articulates with the medial side of the talus.

Attachments on the Tibia A. The muscles inserted into the tibia are as follows (Figs. 3.36, 3.37) 1. The pull of the quadriceps femoris is transmitted to the tibia through the ligamentum patellae which is attached to the smooth upper part of the tuberosity of the tibia. The attachment may extend to the rough lower part of the tuberosity also. 2. The sartorius, the gracilis, and the semitendinosus have linear vertical areas of insertion on the upper part of the medial surface. The area for the sartorius is most

Fig. 3.36. Right tibia, showing attachments, seen from the front.

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anterior and that for the semitendinosus is most posterior. The line for the gracilis is higher than that for the semitendinosus. 3. The semimembranosus is inserted into the 3 posterior and medial aspects of the medial condyle. 4. The popliteus is inserted into the posterior surface of the shaft, on the triangular area above the soleal line.

B. The muscles taking origin from the tibia are as follows 1. The tibialis anterior arises from the upper two thirds of the lateral surface of the shaft. 2. The soleus arises from the soleal line, and from the middle one third of the medial border of the shaft. 3. The tibialis posterior arises from the upper two thirds of the lateral part of the posterior surface of the shaft, below the soleal line. 4. The flexor digitorum longus arises from the medial part of the posterior surface of the shaft below the soleal line.

C. Other attachments on the Tibia

Fig. 3.37. Right tibia, showing attachments, seen from behind.

1. The capsular ligament of the knee joint is attached to the condyles of the tibia a little below the margins of the articular sufaces. Postero -laterally, there is a gap in the attachment of the capsule for passage of the tendon of the popliteus. Anteriorly and laterally, the capsule is represented by the lateral patellar retinaculum; and anteriorly and medially the capsule is represented by the medial patellar retinaculum. In the region of

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the tuberosity the attachment of the capsule is replaced by that of the ligamentum patellae. 2. The intercondylar area, on the superior aspect of the upper end of the tibia, has the following attachments (in anteroposterior sequence)(See Fig. 3.38). (a) Anterior end of medial meniscus. (b) Anterior cruciate ligament. (c) Anterior end of lateral meniscus. (d) Posterior end of lateral meniscus. (e) Posterior end of medial meniscus.

Fig. 3.38. Right tibia, showing attachments, seen from above. Compare with figure 3.30.

(f) Posterior cruciate ligament. 3. The margins of the fibular facet give attachment to the capsule of the superior tibiofibular joint. 4. The iliotibial tract is attached to a triangular impression on the anterolateral part of the lateral condyle. 5. The tibial collateral ligament (of the knee joint) is attached to a rough area on the medial surface adjoining the upper part of the medial Fig. 3.39. Right tibia, lower end, lateral aspect, showing the area for attachment of the border. interosseous tibiofibular ligament

6. The interosseous membrane is attached to the interosseous border. 7. The rough upper part of the fibular notch gives attachment to the interosseous tibiofibular ligament (Fig. 3.39). 8. The articular capsule of the ankle joint is attached to the margins of the articular surface on the lower end of the bone. 9. The medial end of the superior extensor retinaculum of the ankle is attached to the anterior border of the shaft (near its lower end). 10. The upper ‘limb’ of the inferior extensor retinaculum is attached to the anterior surface of the medial malleolus.

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11. The flexor retinaculum is attached to the posterior surface of the medial malleolus. Some Relations of the Tibia 1. The anterior aspect of the lower end of the tibia (which is continuous with the lateral 3 surface of the shaft) is crossed by the tendons of the following muscles (from medial to lateral side). (a) Tibialis anterior (b) Extensor hallucis longus (c) Extensor digitorum longus. (d) Peroneus tertius. 2. The anterior tibial vessels and the deep peroneal nerve cross the anterior aspect of the lower end of the bone lying between the tendons of the extensor hallucis longus and the extensor digitorum longus. 3. The posterior aspect of the lower end of the tibia is crossed by tendons of the following muscles (from medial to lateral side). (a) Tibialis posterior (b) Flexor digitorum longus (c) Flexor hallucis longus The tendon of the flexor digitorum longus crosses that of the tibialis posterior near the lower end of the bone. 4. The posterior tibial vessels and nerve cross the posterior aspect of the lower end of the bone lying between the tendons of the flexor digitorum longus and the flexor hallucis longus. Ossification of the Tibia The tibia has three centres of ossification. 1. The primary centre (for the shaft) appears in the 7th week of fetal life. 2. A secondary centre for the upper end appears towards the end of fetal life. It fuses with the shaft between the 16th and 18th years. 3. A secondary centre for the lower end appears during the first year, and fuses with the shaft between the 15th and 17th years. 4. A separate centre may exist for the tibial tuberosity.

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The Fibula The fibula has a shaft, an upper end and a lower end (Figs. 3.40 to 3.44). The upper end is irregularly expanded in all directions. In contrast the lower end is flattened from side to side and forms the lateral malleolus. The medial side of the malleolus bears a triangular articular surface (for the talus)(Figs. 3.40, 3.41). Just behind this articular surface the malleolus shows a deep malleolar fossa (Fig. 3.41); and this fact enables the anterior and posterior aspects of the bone to be distinguished from one another. The side to which a fibula belongs can be determined with the help of the information given above.

The Upper End The upper end of the fibula is also called the head. Its posterior and lateral part shows an upward projection called the styloid process. In front of, and medial to, the styloid process the head shows a circular facet for articulation with the tibia (to form the superior tibiofibular joint). The facet is directed upwards and medially. The part of the bone immediately below the head is called the neck.

The Lower End The lower end of the fibula is called the lateral malleolus. It has a convex lateral surface that can be felt through the overlying skin. This surface is continuous above with a triangular area on the shaft. The medial surface of the malleolus bears a triangular facet, the apex of the triangle being directed downwards. This facet articulates with the lateral surface of the talus and forms part of the ankle joint. Just above the facet the lower part of the shaft shows a rough area. Behind the facet the Fig. 3.40. Right fibula seen from the front.

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Fig. 3.41. Right fibula, medial aspect.

Fig. 3.42. Right fibula seen from behind.

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medial surface of the malleolus shows a deep malleolar fossa. The lower end also has a posterior surface which has a shallow groove on it. It may be noted that the lateral malleolus projects to a lower level than the medial malleolus (of the tibia).

The Shaft The surfaces and borders of the shaft show considerable variation from bone to bone and may be difficult to identify. To trace them it is important to first orientate the bone correctly by examining the lower end as described above. The shaft has three borders: anterior, posterior and interosseous (or medial). The anterior border is sharp (Fig. 3.40). It begins just below the anterior aspect of the head. Near its lower end it turns laterally to join the apex of the triangular area of the shaft already identified above the lateral malleolus. The lowest part of the anterior border forms the posterior margin of the triangle.

Fig. 3.43. Right fibula, lower part, lateral aspect.

The upper end of the posterior border lies in line with the styloid process (Fig. 3.42). Its lower end reaches the medial part of the posterior surface of the lateral malleolus. The interosseous border lies very near the anterior border (Figs. 3.40, 3.44) and may be indistinguishable from the latter in the upper part of the shaft. When traced downwards it passes medially and merges with the upper part of the rough area above the talar facet of the lateral malleolus. The lateral surface of the fibula lies between the anterior and posterior borders. Because of the lateral inclination of the lower part of the anterior border the lower part of the lateral surface faces backwards and becomes continuous with the posterior aspect of the lateral malleolus. The medial surface lies between the anterior and interosseous borders. It is very narrow in the upper half of the shaft. Its lower broader

Fig. 3.44. Transverse sections across the shaft of the right fibula to show its borders and surfaces. A. Through upper part. B. Through lower part.

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part faces as much forwards as medially. This surface is, therefore, sometimes called the anterior surface. The posterior surface lies between the interosseous and posterior borders. It occupies a very large area of the surface of the shaft (Fig. 3.44). Over its upper three fourths it is divided into two distinct parts, medial and lateral, by a vertical ridge called the medial crest (Fig. 3.41). This ridge is more prominent than the interosseous or posterior borders. The medial part of the posterior surface is deeply concave and faces forwards and medially. The lateral part of the posterior surface faces posteriorly in its upper part and medially in its lower part (Fig. 3.44). The lowest part of the posterior surface lies just above the talar facet of the lateral malleolus. This part is roughened for attachment of a strong ligament that connects the fibula to the tibia.

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Attachments on the Fibula A. The muscles attached to the fibula are as follows (Figs. 3.45 to 3.47) 1. The biceps femoris is inserted into the head of the fibula. The attachment is through two separate slips that are separated by the fibular collateral ligament of the knee joint. 2. The narrow medial surface gives origin to the following: (a) The extensor digitorum longus arises from the upper three-fourths of this surface. (b) The peroneus tertius arises from an area on the medial surface below that for the extensor digitorum longus. (c) The extensor hallucis longus arises from the middle two-fourths of the medial surface,

Fig. 3.45. Right fibula, showing attachments, seen from the front.

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Fig. 3.46. Right fibula showing attachments, seen from the medial side.

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Fig. 3.47. Right fibula showing attachments, seen from behind.

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medial to the origin of the extensor digitorum longus. 3. The lateral surface gives origin to the following: (a) The peroneus longus arises from the upper two-thirds of the lateral surface. Part of the muscle also arises3from the lateral aspect of the head of the fibula. The common peroneal nerve lies between the two areas of origin. (b) The peroneus brevis arises from the lower two thirds of the lateral surface. 4. The following muscles are attached to the posterior surface (Fig. 3.46): (a) The tibialis posterior arises from the upper two thirds of the medial part of the posterior surface. (b) The soleus arises from the posterior aspect of the head and from the upper one-fourth of the lateral part of the posterior surface. (c) The flexor hallucis longus arises from the lower twothirds of the lateral part of the posterior surface.

B. Other attachments on the fibula are as follows 1. The capsule of the superior tibiofibular joint is attached to the margins of the tibial facet. 2. The fibular collateral ligament of the knee joint is attached on the lateral aspect of the head (in between the two slips of the biceps femoris). 3. The interosseous membrane is attached to the interosseous border.

Fig. 3.48. Right fibula showing attachments, seen from the lateral side.

4. The interosseous ligament of the inferior tibiofibular joint is attached to a triangular area just above the malleolar articular surface. 5. The posterior tibiofibular and posterior talofibular ligaments are attached to the malleolar fossa.

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6. The superior extensor retinaculum of the ankle is attached to the anterior border of the triangular area present above the lateral malleolus. 7. The superior peroneal retinaculum is attached to the posterior margin of the lateral malleolus.

Some Relations of the Fibula 1. The common peroneal nerve winds round the lateral aspect of the neck of the fibula (Fig. 3.47). 2. The tendons of the peroneus longus and the peroneus brevis pass downwards just behind the lateral malleolus (Fig. 3.46).

Ossification of the Fibula The fibula has three centres of ossification. 1. The primary centre, for the shaft, appears in the 8th fetal week. 2. A secondary centre for the upper end appears in the 3rd or 4th year; and fuses with the shaft between the 17th and 19th years. 3. A secondary centre for the lower end appears in the first year; and fuses with the shaft between the 15th and 17th years. Note: In most long bones the secondary centre that appears first is the last to fuse. The fibula is an exception in that the centre which appears first (for the lower end) is also the first to fuse. Compare with the tibia.

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The Skeleton of the Foot 3 The skeleton of the foot is seen from above (dorsal aspect) in figure 3.49, and from below (plantar aspect) in figure 3.50. The posterior half (or so) of the foot is made up of seven tarsal bones. The largest tarsal bone is called the calcaneus: it is the bone that forms the heel. Placed above the calcaneus there is another large bone called the talus. The talus articulates with the lower ends of the tibia and fibula to form the ankle joint. Anterior (or distal) to the calcaneus and the talus there are two bones of intermediate size. These are the navicular bone placed medially, and the cuboid bone placed laterally. Distal to the navicular bone there are three smaller bones. These are the medial cuneiform, the intermediate cuneiform, and the lateral cuneiform bones. Anterior to the tarsal bones we see five metatarsal bones. Distal to the metatarsal bones there are the phalanges: three (proximal, middle, distal) for each digit except the great toe which has only two phalanges, proximal and distal. We will now take up the consideration of individual bones of the foot. Many of the features to be described can be identified in the articulated foot (Figs. 3.49, 3.50), and these are the ones that need to be known for understanding the attachments of various structures. Some further details can be seen only on isolated bones. Most teachers of anatomy no longer expect undergraduate students to be able to assign individual bones to the right or left side. This information is included for the use of postgraduate students, or for the occasional undergraduate student who may wish to use it. However, every student should be able to correctly orientate the calcaneus or the talus and to determine its side.

PLEASE STUDY THE FIGURES ON THE FOLLOWING TWO PAGES AND MOVE ON TO TEXT ON PAGE 96

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Fig. 3.49. Skeleton of the foot seen from above (dorsal aspect)

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Fig. 3.50. Skeleton of the foot seen from below (plantar aspect)

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The Calcaneus The calcaneus can be correctly orientated, and its side determined using the following information (Figs. 3.49, 3.50 to 3.52) . (1) The bone is elongated anteroposteriorly. The anterior aspect is easily distinguished from the posterior as it is covered by a large articular facet, while the posterior aspect is non-articular. (2) The superior aspect can be distinguished from the inferior as it bears three facets, while the inferior aspect is nonarticular. (3) The medial aspect can be distinguished from the lateral aspect as it bears a prominent projection. Having orientated the bone correctly the following facts can now be appreciated. The calcaneus has anterior, posterior, superior, inferior, medial and lateral surfaces. The anterior surface is fully covered by a large articular facet for the cuboid bone. The posterior surface is non-articular. It is divisible into upper, middle and inferior parts. The lateral surface is more or less flat. Its anterior part shows a small elevation called the peroneal trochlea (or tubercle). The anterosuperior and the posteroinferior aspects of the tubercle are grooved. The medial surface is easily distinguished as it bears a large projection called the sustentaculum tali that projects medially from its anterior and upper part. The inferior aspect of the sustentaculum tali is marked by a groove. The superior or dorsal surface bears three facets: anterior, middle and posterior that articulate with corresponding facets on the talus. The middle facet lies on the upper surface of the sustentaculum tali. It is separated from the posterior facet by a deep groove called the sulcus calcanei. In the articulated foot the sulcus calcanei comes into apposition with a similar groove on the talus (called the sulcus tali), to form the sinus tarsi.

Fig. 3.51. Right calcaneus seen from above.

Fig. 3.52. Right calcaneus seen from below.

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The plantar (or inferior) surface of the calcaneus shows a prominence in its posterior part called the calcaneal tuberosity. The lateral and medial parts of the tuberosity extend further forwards than its central part and are called the lateral and medial processes, respectively, of the tuberosity. The anterior part of the plantar surface shows another elevation called the anterior tubercle.

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The Talus The talus can be orientated correctly, and its side determined using the following information (Figs. 3.49, 3.50, 3.53 to 3.56). (1) The bone is elongated antero posteriorly. The anterior end (or head) can be distinguished from the posterior end as it is rounded and has a large convex articular surface. (2) The superior aspect of the bone bears a large pulley shaped surface that is convex upwards. The inferior aspect bears three facets. (3) The lateral surface bears a large triangular facet, while the medial side shows a ‘comma’ shaped facet. The talus is seen from above in figure 3.53. In this figure we see that the bone has a head, a neck and a body. The distal surface of the head has a large convex surface that articulates with the navicular bone. The upper surface of the body is covered by a large trochlear articular surface which articulates with the lower end of the tibia. This surface is convex from front to back, and concave from side to side. The lateral and medial sides of the bone are shown in figures 3.54 and 3.55 respectively. The lateral surface bears a large triangular facet for articulation with the lateral malleolus of the fibula, while the medial surface bears a ‘comma’ shaped facet that is broad anteriorly and

Fig. 3.53. Right talus, seen from above.

Fig. 3.54. Right talus, seen from the lateral side.

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are three facets–anterior middle and posterior, that articulate with corresponding facets on the upper surface of the calcaneus. The middle and posterior facets are separated by a deep groove called the sulcus tali. We have already seen that, along with the sulcus calcanei, the sulcus tali forms the sinus tarsi. Medial to the anterior calcaneal facet the lower aspect of the head of the talus has an area that rests on the plantar calcaneonavicular ligament.

The Navicular Bone Fig. 3.55. Right talus, seen from the medial side.

The navicular bone articulates proximally with the head of the talus, distally with the three cuneiform bones, and laterally with the cuboid (Figs. 3.49, 3.50, 3.57). The medial part of the bone has a projection called the tuberosity.

Fig. 3.56. Right talus seen from below.

tapers off posteriorly. This facet articulates with the medial malleolus of the tibia. The lower and posterior part of the body of the talus projects backwards. This projection is called the posterior process. A groove divides this process into medial and lateral tubercles. When the talus is viewed from below (Fig. 3.56) we see that the articular area on the head, for the navicular bone, extends on to the inferior aspect of the head. Behind this there

Fig. 3.57. Right navicular bone. A. Proximal aspect. B. Distal aspect.

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The side to which a navicular bone belongs can be determined as follows. (a) The proximal surface is covered by a single large concave articular facet for the head of the talus. The distal surface has an articular surface that is subdivided by ridges into three triangular areas for the three cuneiform bones.

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(b) The dorsal surface is convex, while the plantar surface is concave. Both surfaces are rough. (c) The medial and lateral aspects of the bone can be distinguished by the fact that the tuberosity is directed downwards and medially; and by the fact that the lateral surface usually has a facet for the cuboid bone.

The Cuboid Bone The cuboid bone articulates proximally with the calcaneus; distally with the fourth and fifth metatarsal bones; and medially with the navicular and lateral cuneiform bones (Figs. 3.49, 3.50, 3.58). The lateral and plantar aspects of the bone show a groove that is limited posteriorly by a ridge. The lateral end of this ridge forms a projection called the tuberosity. The side to which a given cuboid bone belongs can be determined by the following: (a) The proximal end bears a large concavoconvex facet for the calcaneus; while the distal end bears an articular surface that is divided into two parts for the 4th and 5th metatarsal bones. (b) The plantar or inferior surface can be distinguished from the dorsal surface as it bears a deep groove that is limited posteriorly by a ridge.

Fig. 3.58. Right cuboid bone. A. Plantar aspect. B. Lateral aspect. C. Medial aspect.

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(c) The lateral aspect of the bone can be identified by the fact that the groove on the plantar surface extends onto the lateral surface also. Further, the lateral end of the ridge is enlarged to form the tuberosity. The medial surface bears a facet for the lateral cuneiform bone, and occasionally one for the navicular bone.

The Medial Cuneiform Bone The medial cuneiform bone is the largest of the cuneiform bones (Figs. 3.49, 3.50, 3.59). It can be distinguished by the fact that it bears a large kidney shaped facet on one side. It articulates proximally with the navicular bone; distally with the first metatarsal bone; and laterally with the intermediate cuneiform and second metatarsal bones. The side to which a given medial cuneiform bone belongs can be determined as follows: (a) The dorsal surface is narrower than the plantar surface. Both are non-articular. (b) The proximal end bears a piriform facet (for the navicular bone), while the distal surface bears a kidney shaped facet (for the first metatarsal). (c) The medial surface is non-articular, while the lateral surface bears articular areas for the intermediate cuneiform and second metatarsal bones.

The Intermediate Cuneiform Bone The intermediate cuneiform bone is the smallest of the cuneiform bones. It is shaped like a typical wedge (Figs. 3.49, 3.50, 3.60). It articulates proximally with the navicular bone, distally with the second metatarsal bone, medially with the medial cuneiform bone, and laterally with the lateral cuneiform bone. The side to which an intermediate cuneiform bone belongs can be determined as follows: (a) The dorsal surface is wide, while the plantar surface is narrow. (b) The medial surface bears an L-shaped facet (for the medial cuneiform), while the Fig. 3.59. Right medial cuneiform bone. A. Distal aspect. B. Lateral aspect.

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with the third metatarsal bone; medially with the intermediate cuneiform and second metatarsal bones; and laterally with the cuboid and fourth metatarsal bones (Figs. 3.49, 3.50, 3.61).

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Fig. 3.60. Right intermediate cuneiform bone. A. Proximal aspect. B. Medial aspect. C. Lateral aspect.

lateral side bears a vertical facet (for the lateral cuneiform). (c) The proximal and distal aspects are both fully covered by triangular facets. The proximal aspect can be distinguished from the distal by looking at the lateral surface. The vertical facet for the lateral cuneiform is placed along the proximal margin of this surface. The distal part of the lateral surface is non-articular.

The Lateral Cuneiform Bone The lateral cuneiform bone articulates proximally with the navicular bone; distally

Fig. 3.61. Right lateral cuneiform bone. A, Proximal aspect.B. Distal aspect. C. Lateral aspect. D. Medial aspect.

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The side to which a particular lateral cuneiform bone belongs can be determined as follows: (a) The dorsal surface is wider than the plantar surface. (b) The proximal and distal surfaces can be distinguished by the fact that the entire distal surface is covered by a triangular facet (for the 3rd metatarsal); but the proximal surface is covered by a smaller facet (for the navicular) which is confined to the dorsal two thirds of the surface.

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contrast to the metacarpal bones which are numbered from lateral to medial side). The metatarsal bones are similar in structure to the metacarpal bones. Each bone has a distal end or head; a proximal end or base and an intervening shaft. The head is rounded. The base is enlarged and has proximal, dorsal, plantar, medial and lateral surfaces. The shaft is slightly convex on its dorsal side and concave on the plantar side.

Articulations of the metatarsal bones

(c) Both the medial and lateral surfaces bear facets, but these are larger and more prominent on the medial aspect. For details of the shape and number of these facets see figure 3.61.

The head of each metatarsal bone articulates with the proximal phalanx of the digit concerned. The articulations of the bases of the metatarsal bones are as follows.

The Metatarsal Bones

The first metatarsal bone has a large kidney shaped facet on the proximal surface of its base (Fig. 3.63). This facet articulates with the medial cuneiform bone.

The metatarsal bones are five in number (Figs. 3.49, 3.50, 3.62 to 3.68). They are numbered from medial to lateral side (in

The base of the second metatarsal bone articulates proximally with the intermediate cuneiform bone; medially with the medial cuneiform bone; and laterally with the lateral cuneiform bone and with the base of the third metatarsal bone. The base of the third metatarsal bone articulates proximally with the lateral

Fig. 3.62. Scheme to show the articulations of the metatarsal bones.

Fig. 3.63. Proximal end of the right first metatarsal bone.

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Fig. 3.64. Base of the right second metatarsal bone. A. Medial aspect. B. Lateral aspect.

Fig. 3.65. Base of the right third metatarsal bone. A. Medial aspect. B. Lateral aspect.

Fig. 3.64. Base of the right second metatarsal bone. A. Medial aspect. B. Lateral aspect.

cuneiform bone; medially with the second metatarsal bone; and laterally with the fourth metatarsal bone. The base of the fourth metatarsal bone articulates proximally with the cuboid bone; medially with the lateral cuneiform bone and with the base of the third metatarsal; and laterally with the base of the fifth metatarsal bone. The fifth metatarsal bone articulates proximally with the cuboid bone and medially with the fourth metatarsal bone.

Identification of individual metatarsal bones 1. The first metatarsal bone is easily distinguished from the others because it is short and thick and has a large kidney shaped facet on the proximal surface of the base (Fig. 3.63). 2. The fifth metatarsal bone is also easily distinguished because it is the only metatarsal bone having a tuberosity (on the lateral side of its base). 3. The 2nd, 3rd and 4th metatarsal bones can be distinguished from each other by examining their bases.

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Fig. 3.66. Base of the right fourth metatarsal bone. A. Medial aspect. B. Lateral aspect. Fig. 3.67. Base of right fifth metatarsal bone. A. Medial aspect. B. Lateral aspect.

(a) The facet on the proximal surface of the base of the fourth metatarsal is quadrangular, while the facets on the second and third metatarsals are triangular. (b) The triangular facet on the proximal surface of the base of the third metatarsal is flat, while that on the second metatarsal is concave. Additional confirmation about the medial and lateral sides of the metatarsal bones can be obtained by examining facets present on the medial and lateral sides of their bases. These are shown in figures 3.64 to 3.67. However, it may be noted that these facets are subject to considerable variation and may be misleading.

Determining the side to which a metatarsal bone belongs We have seen above that the proximal and distal ends of a metacarpal bone are easily distinguished as the proximal end forms the enlarged base, while the distal end bears a rounded head. Similarly, the dorsal and plantar aspects of the bone are evident from the fact that the plantar aspect of the shaft is concave. It follows that the side of a given bone can be determined if we can distinguish between the medial and lateral aspects of the bone. The medial and lateral sides of the first metatarsal bone can be distinguished by examining the kidney shaped facet on its base. The ‘hilum’ of the ‘kidney’ is directed laterally.

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Fig. 3.68. Metacarpal and metatarsal bones compared.

The medial and lateral aspects of the second to fifth metatarsal bones can be distinguished by examining the dorsal side of the base. The proximal end of the base is always placed oblique to the long axis of the shaft, and the lateral side of the base extends proximally for a greater distance than the medial side.

Distinguishing metacarpal and metatarsal bones from each other

Fig. 3.69. Skeleton of the right foot, showing attachments, seen from the dorsal aspect.

Students often confuse metacarpal and metatarsal bones with each other. They can be easily distinguished by comparing the relative size of the head and the base (Fig. 3.68). These are approximately equal in metacarpal bones, but in metatarsal bones the base is much larger than the head.

The Phalanges of the Foot The phalanges of the foot are arranged on a pattern similar to that in the hand (Figs. 3.49, 3.50). There are three phalanges in each toe except the great toe: proximal, middle and distal. The great toe has only two phalanges, proximal and distal. The phalanges of the foot are similar in shape to those of the hand, but are much shorter and thinner than the latter.

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Attachments on the Skeleton of the Foot A. The attachments on the dorsal aspect of the skeleton of the foot are as follows (Fig. 3.69) 1. The gastrocnemius, the soleus and the plantaris are inserted through the tendocalcaneus into the middle of the posterior surface of the calcaneus. 2. The peroneus brevis is inserted into the lateral side of the base of the fifth metatarsal bone. 3. The peroneus tertius is inserted on the dorsal surface of the base of the fifth metatarsal bone. 4. The extensor digitorum longus ends in four tendons, one for each of the lateral four digits. The tendon for each digit ends in three slips, one intermediate and two collateral. The intermediate slip is inserted into the base of the middle phalanx; and the collateral slips are inserted into the base of the distal phalanx. 5. The extensor hallucis longus is inserted into the dorsal aspect of the base of the distal phalanx of the great toe. 6. The extensor digitorum brevis takes origin from the anterior part of the superior and lateral aspects of the calcaneus. 7. The extensor hallucis brevis (a part of the extensor digitorum brevis) is inserted into the dorsal surface of the base of the proximal phalanx of the great toe

Fig. 3.70. Skeleton of right foot, showing attachments. seen from the ventral aspect.

B. The tendons descending from the leg to gain insertion on to the plantar aspect of the skeleton of the foot are as follows (Fig. 3.70) 1. The tibialis posterior is inserted mainly into the tuberosity of the navicular bone and the medial cuneiform bone.

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Slips from the tendon (not shown in the diagram) also reach the sustentaculum tali, the intermediate cuneiform bone, the lateral cuneiform bone, the cuboid, and the bases of the 2nd, 3rd and 4th metatarsal bones. 2. The tibialis anterior is inserted into the medial cuneiform bone (on its medial and plantar 3 aspects) and into the medial side of the base of the first metatarsal bone. 3. The peroneus longus is inserted into the lateral side of the medial cuneiform bone, and into the lateral side of the base of the first metatarsal bone. 4. See peroneus brevis, above. 5. The flexor hallucis longus is inserted into the plantar aspect of the base of the distal phalanx of the great toe. 6. The flexor digitorum longus is inserted into the plantar surfaces of the bases of the distal phalanges of all digits except the great toe.

C. The attachments of intrinsic muscles of the foot (excluding the interossei) on the plantar aspect of the skeleton of the foot are as follows (Fig. 3.70) 1. The flexor digitorum brevis arises from the medial process of the tuberosity of the calcaneus. The muscle ends in four tendons, one for each of the lateral four toes. Each tendon divides into two slips attached to the medial and lateral sides of the middle phalanx of the digit concerned. 2. The flexor digitorum accessorius arises from the calcaneus by two heads. The lateral head arises from the lateral process of the tuberosity, and the medial head from the medial surface, inferior to the groove for the tendon of the flexor hallucis longus. (Note that this muscle does not have a bony insertion). 3. The flexor hallucis brevis arises from the plantar surfaces of the cuboid and lateral cuneiform bones. At its insertion the muscle divides into two parts, medial and lateral, that are attached to the corresponding sides of the base of the proximal phalanx of the great toe. (Also see below). 4. The abductor hallucis takes origin from the medial process of the calcaneal tuberosity. It is inserted into the medial side of the base of the proximal phalanx of the great toe (along with the medial part of the flexor hallucis brevis). 5. The adductor hallucis (oblique head) arises from the bases of the 2nd, 3rd, and 4th metatarsal bones (and also from the sheath of the peroneus longus). (Note: The transverse head of the muscle does not have a bony origin. It arises from the ligaments on the plantar aspect of the metatarsophalangeal joints of the 3rd, 4th, and 5th toes). The muscle is inserted into the lateral side of the base of the proximal phalanx of the great toe (along with the lateral part of the flexor hallucis brevis).

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6. The abductor digiti minimi takes origin from both the lateral and medial processes of the tuberosity of the calcaneus. It is inserted into the lateral side of the proximal phalanx of the 5th toe (along with the flexor digiti minimi brevis). 7. The flexor digiti minimi brevis arises from the plantar surface of the base of the 5th metatarsal bone. It is inserted into the lateral side of the proximal phalanx of the 5th toe (along with the abductor digiti minimi).

D. The attachments of the interossei of the foot are as follows (Figs. 3.71, 3.72) 1. The first plantar interosseous muscle arises from the plantar aspect of the shaft of the third metatarsal bone. The second plantar interosseous muscle has a similar origin from the fourth metatarsal; and the third plantar interosseous muscle from the fifth metatarsal. The plantar interossei are inserted into the medial side of the base of the proximal phalanx of the corresponding digit (and also into the dorsal digital expansion). 2. Each dorsal interosseous muscle arises from the adjacent sides of the shafts of two metatarsal bones as follows: (a) The first muscle from the 1st and 2nd metatarsals. (b) The second muscle from the 2nd and 3rd metatarsals. (c) The third muscle from the 3rd and 4th metatarsals. (d) The fourth muscle from the 4th and 5th metatarsals. The dorsal interossei are inserted as follows. (a) The first muscle on the medial side of the base of the proximal phalanx of the 2nd digit. (b) The second muscle on the lateral side of the base of the proximal phalanx of the 2nd digit. (c) The third muscle on the lateral side of the base of the proximal phalanx of the 3rd digit.

Fig. 3.71. Attachments of plantar interossei.1 to 5. Metatarsal bones.

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(d) The fourth muscle on the lateral side of the base of the proximal phalanx of the 4th digit.

3 E. Other attachments on the bones of the foot. 1. The bones of the foot give attachment to numerous ligaments connected with the ankle, intertarsal, and tarsometatarsal joints; and with the joints of the digits. The more important of these are as follows. (a) The anterior and posterior talofibular ligaments are attached to the lateral side of the talus. (b) The anterior and posterior tibiotalar ligaments are attached on the medial side of the talus. (c) The calcaneofibular ligament is attached to the lateral surface of the calcaneus.

Fig. 3.72. Attachments of dorsal interossei of the foot.1 to 5. Metatarsal bones.

(d) The cervical ligament is attached (above) to the inferolateral aspect of the neck of the talus; and (below) to the superior surface of the calcaneus. (e) The long plantar ligament is attached posteriorly to the plantar surface (tuberosity) of the calcaneus; and anteriorly to the plantar surface of the cuboid bone distal to the groove for the peroneus longus (Fig. 3.70). Some fibres of the ligament reach the bases of the 2nd, 3rd, and 4th metatarsal bones. (f) The short plantar ligament passes from the anterior tubercle of the calcaneus to the cuboid bone (proximal to the groove for the peroneus longus) (Fig. 3.70). (g) The plantar calcaneonavicular ligament or spring ligament passes from the anterior margin of the sustentaculum tali of the calcaneus to the plantar surface of the navicular bone (Fig.3.70). (h) The bifurcate ligament is Y-shaped. The stem of the ‘Y’ is attached (posteriorly) to the upper surface of the calcaneus. The limbs are attached (anteriorly) to the dorsal aspect of the cuboid and navicular bones. (i) The interosseous talocalcaneal ligament passes from the sulcus tali (on the talus) to the sulcus calcanei (on the calcaneus).

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2. The lateral end of the inferior extensor retinaculum (of the ankle) is attached to the upper surface of the calcaneus. 3. The lower end of the flexor retinaculum (of the ankle) is attached to the medial surface of the calcaneus. 4. The peroneal retinacula are attached to the lateral surface of the calcaneus. 5. The fibrous flexor sheath of each digit is attached to the sides of the phalanges, on the plantar aspect.

Ossification of the Bones of the Foot The calcaneus has one main centre of ossification that appears in the third fetal month; and a secondary centre (for a scale like epiphysis that covers its posterior part) that appears in the 6th to 8th years. All other tarsal bones normally have one centre each which appears as follows. Talus -------------------------- 6th fetal month Cuboid -------------------------- Just before or after birth Medial cuneiform -------------------------- 3rd year Intermediate cuneiform -------------------------- 1st year Lateral cuneiform -------------------------- 1st year Navicular -------------------------- 3rd year

Each metatarsal bone has a primary centre for the shaft appearing in the 9th or 10th fetal week. The first metatarsal has a secondary centre for its base appearing in the 3rd year. The other metatarsals have secondary centres for their heads (not bases) appearing in the 3rd or 4th year. The secondary centres unite with the shafts between the 17th and 20th years. Each phalanx has a primary centre for the shaft (appearing in the 7th to 15th fetal weeks); and a secondary centre for the base (appearing between the 2nd to 8th years) which unites with the shaft by the 18th year.

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4 3

The Vertebral Column

Structure of a Typical Vertebra The parts of a typical vertebra are best seen by examining a vertebra from the mid-thoracic region. Such a vertebra is seen from above in figure 4.1 and from behind in figure 4.2. A lateral view of two such vertebrae is shown in figure 4.3. The following parts can be distinguished. (1) The body lies anteriorly. It is shaped like a short cylinder, being rounded from side to side, and having flat upper and lower surfaces that are attached to those of adjoining vertebrae through intervertebral discs (Fig. 4.3). (2) The pedicles (right and left) are short rounded bars that project backwards, and somewhat laterally, from the posterior part of the body. (3) Each pedicle is continuous, posteromedially, with a vertical plate of bone called the lamina. The laminae of the two sides pass backwards and medially to meet in the middle line. The pedicles and laminae together constitute the vertebral arch. (4) Bounded anteriorly by the posterior aspect of the body, on the sides by the pedicles, and behind by the laminae, there is a large vertebral foramen. Each vertebral foramen forms a short segment of the vertebral canal that runs through the whole length of the vertebral column and transmits the spinal cord. Fig. 4.1. Typical vertebra seen from above.

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(5) Passing backwards (and usually downwards) from the junction of the two laminae, there is the spine (or spinous process). (6) Passing laterally (and usually somewhat downwards) from the junction of each pedicle and the corresponding lamina there is a transverse process. The spinous and transverse processes serve as levers for muscles acting on the vertebral column. When the vertebrae are viewed from the lateral side (Fig. 4.3) we see certain additional features. Fig. 4.2. Typical vertebra seen from behind. (7) Projecting upwards from the junction of the pedicle and the laminae there is, on either side, a superior articular process; and projecting downwards there is an inferior articular process. Each process bears a smooth articular facet: the superior facet is directed posteriorly and somewhat laterally, and the inferior facet is directed forwards and somewhat medially.

The superior facet of one vertebra articulates with the inferior facet of the vertebra above it. Two adjoining vertebrae, therefore, articulate at three joints: two between the right and left articular processes and one between the bodies of the vertebrae (through the intervertebral disc).

Fig. 4.3. Typical vertebrae seen from the lateral side. (Costal facets, for ribs, are shown on the bodies and transverse processes: they are present only in the thoracic region).

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(8) In figure 4.3 note that the pedicle is much narrower than the body (in vertical diameter) and is attached nearer its upper border. As a result there is a large inferior vertebral notch below the pedicle. The notch is bounded in front by the posterior surface of the body of the vertebra, and behind by the inferior articular process. Above the pedicle there is a much shallower superior vertebral notch. The superior and inferior notches of adjoining vertebrae join to form 3 the intervertebral foramina which give passage to spinal nerves emerging from the spinal cord.

Distinguishing features of Typical Cervical, Thoracic and Lumbar Vertebrae The cervical, thoracic and lumbar vertebrae can be easily distinguished from one another because of the following characteristics. (a) The transverse process of a cervical vertebra is pierced by a foramen called the foramen transversarium (Fig. 4.4). (b) The thoracic vertebrae bear costal facets for articulation with ribs. These are present on the sides of the vertebral bodies and on the transverse processes (Fig. 4.3). (c) A lumbar vertebra (Fig. 4.6) can be distinguished by the fact that it neither has foramina transversaria nor does it bear facets for ribs. It is also recognized by the large size of its body. We may now consider additional differences between cervical, thoracic and lumbar vertebrae.

Fig. 4.4. Typical cervical vertebra seen from above.

(1) The vertebral bodies progressively increase in size from above downwards. They are, therefore, smallest in the cervical vertebrae and largest in the lumbar vertebrae. In shape the body is oval in the cervical and lumbar regions and triangular or heart shaped in the thoracic region. The upper and lower surfaces of the bodies are more or less flat in the thoracic and lumbar region. In cervical vertebrae the upper surface of the body is concave

Fig. 4.5. Typical cervical vertebra seen from the anterolateral side.

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from side to side (Fig. 4.5): the posterolateral parts of its edge are raised to form distinct lips. As a result of this the superior vertebral notch is prominent in cervical vertebrae, but is barely perceptible in thoracic vertebrae (Fig. 4.3). In the thoracic region the head of a typical rib articulates with the sides of the bodies of two vertebrae (Fig. 4.7). For this purpose each side of the body of a typical thoracic vertebra bears two costal facets, upper and lower, adjoining its upper and lower borders (Fig. 4.3). Each of these is really only half a facet (demifacet), the other half being on the adjoining vertebra. The upper facet is large and articulates with the numerically corresponding Fig. 4.6. Typical lumbar vertebra seen from above. rib. The lower, smaller facet articulates with the next lower rib. (2) The vertebral foramen is triangular and large in cervical vertebrae (Fig. 4.4). In the lumbar vertebrae also it is triangular (Fig. 4.6), but in thoracic vertebrae it is small and circular or oval (Fig. 4.1). These variations in size correspond with those of the spinal cord which is largest (in diameter) in the cervical region. (3) The pedicles are long and directed backwards and laterally in the cervical region (Fig. 4.4). In the thoracic region they pass almost directly backwards (Fig. 4.1). They are thick and short in the lumbar region and are directed backwards and somewhat laterally (Fig. 4.6).

Fig. 4.7. Scheme showing the numerical relationship of thoracic vertebrae to ribs.

(4) The laminae of cervical vertebrae are long (transversely) and narrow (vertically) (Fig. 4.4). In the thoracic region they are short (transversely) and so broad (vertically) that the laminae of adjacent vertebrae overlap (Figs. 4.1, 4.2). In the lumbar region also they are short and broad, but do not overlap (Fig. 4.6). (5) The spinous processes are short and bifid in a typical cervical vertebra (Fig. 4.4). They are long and project downwards in the thoracic region (Fig. 4.3). In lumbar vertebrae they are

Fig. 4.8. Typical lumbar vertebra seen from the lateral side.

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Fig. 4.10. Fifth lumbar vertebra seen from above.

large and quadrangular: they are more or less horizontal and have a thick posterior edge (Fig. 4.8).

Fig. 4.9. Cervical (A), thoracic (B), and lumbar (C) transverse processes showing the parts derived from the costal elements (red shading).

(6) The transverse processes of typical cervical vertebrae (Fig. 4.9A) are relatively short and, as mentioned earlier, they are pierced by foramina transversaria. The part of the process in front of the foramen is called the anterior root; and the part behind it is called the posterior root. The part lateral to the foramen is usually called the costotransverse bar, but it is more correct to call it the intertubercular bar. The anterior and posterior roots end in thickenings called the anterior and posterior tubercles respectively. When viewed from the lateral side the transverse process is seen to be grooved (Fig. 4.5). The cervical nerves lie in these grooves after they pass out of the intervertebral foramina. The transverse processes of a typical thoracic vertebra are large with solid blunt ends (Figs. 4.1, 4.3). They are directed backwards and

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laterally. Each process lies just behind the corresponding rib and bears a prominent facet for articulation with the rib. The lumbar transverse processes are relatively small and often have tapering ends. The posteroinferior aspect of the root of each transverse process bears an elevation called the accessory process (Fig. 4.9C). Although proper ribs are formed only in the thoracic region, rudimentary ribs are formed in the cervical and lumbar regions during fetal life. These become fused with the true transverse processes. The part of the transverse process derived from the rudimentary rib is called the costal element. In the cervical region (Fig. 4.9A) the costal element forms the anterior root, the costotransverse bar and both the anterior and posterior tubercles. In the lumbar region (Fig. 4.9C) the costal element forms a strip along the anterior margin of the transverse process.

Fig. 4.11. Scheme to show the orientation of the articular facets of cervical vertebrae (lateral view).

Fig. 4.12. Scheme to show the orientation of the articular facets of thoracic vertebrae (lateral view).

(7) The direction of the articular facets is variable. It is shown diagramatically in figures 4.11 to 4.13. In the cervical region the facets are flat. The superior facets are directed equally backwards and upwards (Also see figure 4.4). The inferior facets are directed forwards and downwards (Also see figure 4.5). In the thoracic region again (Fig. 4.12) the facets are flat, and here they are almost vertical. The superior facets face backwards,

Fig. 4.13. Scheme to show the orientation of the articular facets of lumbar vertebrae. The facets are seen from above. The inferior processes are cut across.

slightly upwards and slightly laterally (Also see Fig. 4.2). The inferior facets face forwards, slightly downwards and slightly medially. In the lumbar region the facets are vertical. They are curved from side to side (Fig. 4.13). The superior facets are slightly concave (Also see Fig. 4.6) and are directed equally backwards and medially. The inferior facets are slightly convex, and are directed equally forwards and laterally (Also see Fig. 4.8). Each superior articular process of a lumbar vertebra bears a rough projection called the mamillary process, on its posterior border.

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In the cervical region the superior and inferior articular processes form a solid articular pillar that helps to transmit some weight from one vertebra to the next lower one. This is not so in the thoracic and lumbar regions.

3 Attachments on Vertebrae Vertebrae give attachment to numerous muscles and ligaments. The muscles attached to vertebrae vary from vertebra to vertebra, and no useful purpose is served by trying to list them. The ligaments concerned are those that hold adjoining vertebrae together. Adjoining vertebrae are connected to each other at three joints. There is one median joint between the vertebral bodies, and two joints (one right and one left) between the articular processes. 1. Adjoining vertebral bodies are connected to each other by intervertebral discs, made up of fibrocartilage. Each disc has an outer fibrous part called the annulus fibrosus, and an inner soft part called the nucleus pulposus. 2. The joints between the articular processes are synovial joints. The capsules of these joints are attached along the margins of articular facets.

Fig. 4.14. Scheme to show the position of various ligaments interconnecting adjoining vertebrae.

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3. Apart from the intervertebral discs and the capsular ligaments, adjoining vertebrae are connected to one another by a series of ligaments that are shown schematically in figure 4.14. These ligaments are as follows: (a) The anterior longitudinal ligament passes from the anterior surface of the body of one vertebra to another. Its upper end reaches the basilar part of the occipital bone. (b) The posterior longitudinal ligament is present on the posterior surface of the vertebral bodies (within the vertebral canal). Its upper end reaches the body of the axis beyond which it is continuous with the membrana tectoria. (c) The intertransverse ligaments connect adjacent transverse processes. (d) The interspinous ligaments connect adjacent spinous processes. (e) The supraspinous ligaments connect the tips of the spines of vertebrae from the 7th cervical to the sacrum. (In the neck they are replaced by the ligamentum nuchae). (f) The ligamenta flava (singular = ligamentum flavum) connect the laminae of adjacent vertebrae. The right and left ligaments meet in the middle line.

Fig. 4.15. The atlas (first cervical vertebra) seen from above.

Fig. 4.16. The atlas (first cervical vertebra) seen from below.

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Atpical Cervical Vertebrae The Atlas (First Cervical) Vertebra

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The first cervical vertebra is called the atlas. It looks very different from a typical cervical vertebra as it has no body, and no spine (Figs. 4.15, 4.16). It consists of two lateral masses joined anteriorly by a short anterior arch, and posteriorly by a much longer posterior arch. The arches give the atlas a ring like appearance. A large transverse process, pierced by a foramen transversarium, projects laterally from the lateral mass. The superior aspect of each lateral mass shows an elongated concave facet which articulates with the corresponding condyle of the occipital bone (to form an atlanto-occipital joint). The long axis of the facet runs forwards and medially. The facet may be constricted at its middle or may even be divided into two. Nodding and lateral movements of the head take place at the two (right and left) atlanto-occipital joints. The inferior aspect of each lateral mass (Fig. 4.16) shows a large oval (almost circular) facet for articulation with the corresponding superior articular facet of the axis (second cervical vertebra) to form a lateral atlanto-axial joint. The facet is more or less flat and is directed downwards and medially and somewhat backwards. The medial side of the lateral mass shows a tubercle which gives attachment to the transverse ligament of the atlas (shown in dotted line in figure 4.15). This ligament divides the large foramen (bounded by the lateral masses and the arches) into anterior and posterior parts. The posterior part corresponds to the vertebral foramen of a typical vertebra: the spinal cord passes through it. The anterior part is occupied by the dens (which is an upward projection from the body of the axis). The dens articulates with the posterior aspect of the anterior arch, which bears a circular facet for it. The dens also articulates with the transverse ligament, these two articulations collectively forming the median atlanto-occipital joint. In side to side movements of the head the atlas moves with the skull around the pivot formed by the dens. The anterior arch bears a small midline projection called the anterior tubercle. The posterior arch bears a similar projection, the posterior tubercle, which may be regarded as a rudimentary spine. The upper surface of the posterior arch is grooved by the vertebral artery. The groove is continuous laterally with the foramen transversarium. The transverse processes are large. Their tips are believed to correspond to the posterior tubercles of the transverse processes of a typical cervical vertebra.

Attachments and Relations of the Atlas 1. The vertebral artery passes upwards through the foramen transversarium and then runs medially on the groove over the posterior arch. It is accompanied by the vertebral vein (which is in the form of a plexus), and by a plexus of sympathetic nerve fibres (Fig. 4.17).

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Fig. 4.17. Some structures attached/related to the atlas.

2. The first cervical nerve crosses the posterior arch deep to the vertebral artery and divides here into anterior and posterior primary rami. 3. Structures passing through the vertebral canal include the spinal cord, the meninges, the spinal part of the accessory nerve, and the anterior and posterior spinal arteries.

4. The ligaments attached to the atlas are as follows. (a) The capsules of the atlanto-occipital joints, and those of the atlantoaxial joints are attached along the margins of the corresponding facets. (b) The anterior and the posterior atlanto-occipital membranes are attached to the upper margins of the corresponding arches of the atlas. (c) The transverse ligament is attached to the medial side of the lateral mass. (d) The ligamentum nuchae is attached to the tip of the posterior tubercle. (e) The atlas is attached to the axis by ligaments similar to those between typical cervical vertebrae.

5. The muscles attached to the atlas are as follows. (a) The rectus capitis anterior arises from the front of the lateral mass and from the root of the transverse process. (b) The rectus capitis lateralis arises from the anterior part of the upper surface of the transverse process. (c) The rectus capitis posterior minor arises from the posterior tubercle.

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(d) The obliquus capitis superior arises from the posterior part of the upper surface of the transverse process. (e) The obliquus capitis inferior, and the splenius cervicis are inserted into the inferior aspect of the transverse process.

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(f) The levator scapulae arises from the lateral margin of the transverse process. (g) Some fibres of the upper oblique part of the longus colli are inserted on the anterior tubercle.

The Axis (Second Cervical) Vertebra The most conspicuous feature of the axis, which distinguishes it from all other vertebrae, is the presence of a thick finger like projection arising from the upper part of the body. This projection is called the dens, or odontoid process. We have already seen that the dens fits into the space between the anterior arch of the atlas and its transverse ligament to form the median atlanto-occipital joint. The anterior aspect of the dens bears a convex oval facet (Fig. 4.18) for articulation with the anterior arch. Its posterior aspect shows a transverse groove for the transverse ligament. On either side of the dens the axis vertebra bears a large oval facet for articulation with Fig. 4.18. The atlas (first cervical vertebra) seen from above.

Fig. 4.19. The atlas (first cervical vertebra) seen from below.

the corresponding facet on the inferior aspect of the atlas. The transverse process of the axis lies lateral to this facet. It is small and ends in a single tubercle corresponding to the posterior tubercle of a typical cervical vertebra. The transverse process is pierced by a foramen transversarium which runs upwards and laterally (to correspond with the lateral direction of the vertebral artery as it passes from the axis to the atlas). The pedicles, laminae and spine are thick and strong. The inferior articular facets are placed below the junction of the pedicles and the laminae. They are orientated as in a typical cervical vertebra.

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Attachments and Relations 1. The ligaments attached to the axis are as follows (Fig. 4.20) (a) The apical ligament is attached to the apex of the dens. (b) The right and left alar ligaments are attached to the dens on depressions just below and lateral to the apex. (c) The lower end of the membrana tectoria is attached to the posterior surface of the body. (d) The ligamentum nuchae is attached to the tip of the spine. (e) The axis is connected to the atlas and to the third cervical vertebra through ligaments similar to those between typical vertebrae.

Fig. 4.20. Some structures attached to the axis. The vertebra is viewed from above and behind.

2. The muscles attached to the axis are as follows. (a) The rectus capitis posterior major arises from the thick posterior edge of the spine. (b) The obliquus capitis inferior arises from the side of the spine. (c) The scalenus medius (not shown in the figure) arises from the anterior aspect of the transverse process. (d) The levator scapulae arises from the lateral aspect of the transverse process. (e) The splenius cervicis is inserted into the posterior aspect of the transverse process. (f) The semispinalis cervicis is inserted into the lower part of the spine and of the lamina. (g) The vertical part of the longus colli (not seen in the figure) is attached to the anterior aspect of the body. (h) Other muscles attached to the spine (but not shown) are the multifidus, the spinalis cervicis and the interspinalis.

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The Seventh Cervical Vertebra The seventh cervical vertebra differs from a typical vertebra in having a long thick spinous process which ends in a single tubercle (Fig. 4.21). The tip of the process forms a prominent surface landmark. Because of this fact this vertebra is referred to as the vertebra prominens. The transverse processes are also large and have prominent posterior tubercles. Note that the vertebral artery and vein do not traverse the foramen transversarium of this vertebra. An accessory vertebral vein passes through the foramen.

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Fig. 4.21. Seventh cervical vertebra seen from above.

OTHER ATYPICAL VERTEBRAE First Thoracic Vertebra This vertebra can be distinguished from a typical thoracic vertebra because of the following features (Figs. 4.22, 4.23). It has a small body similar in shape to that of a cervical vertebra. The posterolateral parts of the body are raised (as in cervical vertebrae) and as a result a definite superior vertebral notch can be identified. (This is virtually absent in other thoracic vertebrae). The superior costal facets (on the body) are usually complete as the first rib articulates wholly with this vertebra. The spine is long and horizontal (Fig. 4.23).

Tenth, Eleventh and Twelfth Thoracic Vertebrae These vertebrae tend to resemble the lumbar vertebrae in the shape and size of their bodies, of the vertebral foramina, and of the spines (Fig. 4.24). They can be distinguished from typical thoracic vertebrae by the fact that they have only one costal facet on each side of the body. The tenth vertebra (normally) has a costal facet on each transverse process. The transverse process is large as in typical thoracic vertebrae. Facets on the transverse processes Fig. 4.22. First thoracic vertebra seen from above.

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Fig. 4.23. First thoracic vertebra seen from the lateral side.

are absent in the eleventh and twelfth vertebrae which have small transverse processes. The eleventh and twelfth vertebrae can be distinguished from each other by examining the inferior articular facets. These are of the thoracic type in the eleventh vertebra, but are of the lumbar type in the twelfth vertebra. Further confirmation can be obtained by examining the transverse processes. Those of the twelfth vertebra show superior, inferior and lateral tubercles, which are absent or rudimentary on the eleventh vertebra. Fig. 4.24. Tenth, eleventh and twelfth thoracic vertebrae seen from the lateral side.

Fifth Lumbar Vertebra The fifth lumbar vertebra is the largest of lumbar vertebrae. We have seen that the transverse processes of typical lumbar vertebrae are small and tapering. In contrast the transverse processes of the fifth lumbar vertebra are very large: they form a distinguishing characteristic of this vertebra (Fig. 4.10).

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The Sacrum and Coccyx 3

THE SACRUM

The sacrum lies below the fifth lumbar vertebra. It is made up of five sacral vertebrae that are fused together (Figs. 4.25 to 4.31). It is wedged between the two hip bones and takes part in forming the pelvis (See Fig. 2.1). As a whole the bone is triangular. It has an upper end or base which articulates with the fifth lumbar vertebra; a lower end or apex which articulates with the coccyx; a concave anterior (or pelvic) surface; a convex posterior or (dorsal) surface (Fig. 4.27); and right and left lateral surfaces that articulate with the ilium of the corresponding side (Fig. 4.29). When viewed from the front (Fig. 4.25) the pelvic surface of the sacrum shows the presence of four pairs of anterior sacral foramina. The first foramen is the largest and the fourth the smallest.

Fig. 4. 25. Sacrum seen from the front.

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The foramina separate the medial part of the bone from the lateral part. The medial part is formed by the fused bodies of the sacral vertebrae, while the lateral part represents the fused transverse processes, including the costal elements. The anterior sacral foramina, seen on the pelvic surface, are continued into the substance of the bone and become continuous posteriorly with the posterior sacral foramina that Fig. 4.26. Sacrum seen from above. open on to the dorsal surface. The canals connecting the anterior and posterior foramina open medially into the sacral canal which is a downward continuation of the vertebral canal. When viewed from above (Fig. 4.26) the base of the sacrum is seen to be formed by the first sacral vertebra in which we can recognize a large oval body that articulates with the body of the fifth lumbar vertebra. The body has a projecting anterior margin called the sacral promontory. Behind the body there is a triangular vertebral (or sacral) canal bounded by thick pedicles and

Fig. 4.27. Sacrum seen from behind.

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laminae. Where the laminae meet there is a small tubercle representing the spine. Arising from the junction of the pedicles and laminae there are the superior articular facets that articulate with the inferior articular facets of the fifth lumbar vertebra. Lateral to the body we see the superior surface of the lateral part, that is also called the ala. When the sacrum is viewed from behind (Fig. 4.27) we see the dorsal surface. We can again distinguish medial and lateral parts separated by four pairs of posterior sacral foramina. These foramina give passage to the dorsal rami of sacral nerves. The medial part of the dorsum of the sacrum is formed by the fused laminae of sacral vertebrae. The laminae of the fifth sacral vertebra (sometimes also of the fourth) are deficient leaving an inverted U-shaped or V-shaped gap called the sacral hiatus. The midline is marked by a ridge called the median sacral crest on which four spinous tubercles (representing the spines) can be recognized. Just medial to the dorsal sacral foramina we see four small tubercles that represent fused articular processes: they collectively form the intermediate crest. Lateral to the foramina we see a prominent lateral sacral crest formed by the fused transverse processes. The crest is marked by tubercles which represent the tips of the transverse processes.

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Fig. 4.28. Sacrum seen from below.

Fig. 4.29. Sacrum seen from the lateral side.

The lower end of the bone (apex) bears an oval facet for articulation with the coccyx (Fig. 4.28). At the sides of the sacral hiatus we see two small downward projections called the sacral cornua. They represent the inferior articular processes of the fifth sacral vertebra. They are connected to the coccyx by ligaments. When the sacrum is viewed from the side we see that the pelvic aspect of the bone is concave forwards, while the dorsal aspect is convex backwards. The lateral surface bears a large Lshaped auricular area (or facet) for articulation with the ilium. (It is so called because its shape resembles that of the auricle or pinna). It consists of a cranial limb present on the first sacral vertebra, and a caudal limb that lies on the second and third sacral vertebrae. The area behind the auricular surface is rough and gives attachment to strong ligaments that connect the sacrum to the ilium.

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Sex Differences in the Sacrum The female sacrum is wider and shorter than in the male. This is to be correlated with the fact that the female pelvis is also shorter and broader than the male pelvis. The forward concavity is more pronounced in the female. The auricular surface is shorter in the female. However, for practical purposes the sex of a given sacrum is most easily found out by examining the base. In the female the transverse diameter of the body is approximately equal to the width of the ala; but in the male the diameter of the body is distinctly larger than that of the ala. The attachments on the sacrum are described below.

THE COCCYX The coccyx consists of four rudimentary vertebrae fused together (Figs. 4.30, 4.31). It has pelvic and dorsal surfaces. The base or upper end has an oval facet for articulation with the apex of the sacrum. Lateral to the facet there are two cornua that project upwards and are connected to the cornua of the sacrum by ligaments. The first coccygeal vertebra has rudimentary transverse processes. The remaining vertebrae are represented by nodules of bone.

Attachments on the Sacrum and Coccyx 1.The following muscles are attached. (a) The iliacus arises from the anterolateral part of the upper surface of the ala (or lateral part). (b) The piriformis arises from the pelvic surface. The medial part of the origin is in the form of three digitations that arise from the areas between the sacral foramina.

Fig. 4. 30. Coccyx seen from the front.

Fig. 4.31. Coccyx seen from behind

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(c) The coccygeus is inserted into the lateral side of the pelvic aspect of the last piece of the sacrum and to the coccyx. (d) The levator ani is inserted into the sides of the lower two segments of the coccyx.

3 and (e) The gluteus maximus arises from the lateral margin of the lowest part of the sacrum, that of the coccyx. (f) The erector spinae has a linear U-shaped origin from the dorsal aspect of the sacrum. The medial limb of the ‘U’ is attached to the spinous tubercles, and the lateral limb to the transverse tubercles. (g) The multifidus arises from a large area within the U-shaped origin of the erector spinae.

2. The following ligaments are attached. (a) Ligaments of the joints between the fifth lumbar vertebra and the sacrum correspond to those of other intervertebral joints. (b) The area around the auricular surface gives attachment to the ventral, dorsal and interosseous ligaments of the sacroiliac joint.

Fig. 4. 32. Attachments on the pelvic aspect of the sacrum and coccyx. Some related structures are also shown.

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(c) The iliolumbar ligament is attached to the lateral part of the ala. (d) The sacrotuberous ligament is attached to the lower lateral part of the dorsal surface of the sacrum. (e) The sacrospinous ligament is attached to the lower part of the lateral margin of the sacrum and to the adjoining lateral margin of the coccyx.

Important Relations of the Sacrum 1. The rectum is in contact with the ventral surfaces of the 3rd, 4th and 5th pieces of the sacrum. 2. The ventral surfaces of the first three pieces of the sacrum are covered by peritoneum and give attachment to the sigmoid mesocolon. 3. Deep to the peritoneum and rectum the ventral surface is crossed by the right and left sympathetic trunks, the median sacral vessels, the right and left lateral sacral vessels, and the superior rectal vessels. 4. The ala is covered by the psoas major muscle and is crossed by the lumbosacral trunk. 5. The sacral canal contains the cauda equina, the spinal meninges and the filum terminale. The subarachnoid and subdural spaces end at the level of the middle of the sacrum.

Fig. 4.33. Attachments of muscles on the posterior aspect of the sacrum and coccyx.

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6. The ventral and dorsal sacral foramina give passage to the corresponding rami of sacral nerves. Ossification of the Vertebral Column A typical vertebra has three primary centres of ossification. One centre appears in the3body and one in each half of the neural arch. These centres appear between 9 and 12 weeks of fetal life (at different times in different parts of the vertebral column.) The posterolateral parts of the body of the vertebra are ossified by extension from the centres for the neural arches. The remaining part of the body is called the centrum. For some time the centrum is connected to the neural arches by plates of cartilage forming the neurocentral joints. Sometimes the vertebral body may ossify from two primary centres. If one of these centres fails to develop one half of the body may be missing. This condition is called hemivertebra or cuneiform vertebra. The two neural arches fuse (posteriorly) after birth during the first year. They unite with the centrum between the 3rd and 6th years. Five secondary centres appear in each vertebra after puberty. These are: (i) One at the tip of the spinous process. (ii) and (iii) At the tips of transverse processes. (iv) and (v) Centres that form ring shaped epiphyses over the upper and lower surfaces of the vertebral body. The epiphyses derived from the secondary centres fuse with the rest of the vertebra at about 25 years. The atlas vertebra ossifies from three centres, one appearing in each lateral mass and one in the anterior arch. The posterior arch is formed by extension from the centre for the lateral masses. The axis has five primary centres: one for each half of the vertebral arch, one for the centrum, and two for the dens. The lumbar vertebrae ossify like typical vertebrae, but have additional secondary centres for the mamillary processes. The ossification of the sacrum is complicated. It is significant to note that each piece of the sacrum ossifies like a typical vertebra. The upper pieces have additional centres for the parts derived from the costal elements. The pieces of the sacrum are united to each other by cartilage till the age of about 20 years after which they fuse with each other. Each segment of the coccyx has one primary centre. The centres for most segments appear after birth. The segments usually unite with each other by about the 20th year.

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5 The Sternum and Ribs The Sternum The sternum lies in the anterior wall of the thorax, in the midline (Figs. 5.1 to 5.3). It is elongated vertically. It is flat and has anterior and posterior surfaces. Although it is (by convention) spoken of as a single bone it consists of three separate parts. From above downwards these are the manubrium, the body, and the xiphoid process.

The manubrium joins the body at the manubriosternal joint. The body joins the xiphoid process at the xiphisternal joint. The anterior ends of the upper seven costal cartilages are attached to the right and left margins of the sternum. The first costal cartilage is attached to the lateral margin of the manubrium. The second costal cartilage is attached partly to the manubrium, and partly to the upper end of the body. The third, fourth, fifth and sixth cartilages are attached to the lateral margin of the body. The seventh costal cartilage is attached to the lateral side of the xiphisternal joint. The area of attachment of each cartilage is marked by a notch on the lateral margin of the sternum. The upper border of the manubrium articulates, on either side, with the medial end of the clavicle to form the sternoclavicular joint. It bears prominent clavicular notches for this purpose. Between the right and left clavicular notches there

Fig. 5.1. Sternum and costal cartilages seen from the front.

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is a median depression called the jugular or suprasternal notch. The manubrium and the body of the sternum lie at a slight angle to one another, and because of this fact the manubriosternal junction projects forwards. This projection forms a surface landmark and is often referred to as the sternal angle. The sternal angle forms a useful guide in identifying individual costal cartilages and ribs in the living subject. The body of the sternum consists of four parts or sternebrae that are united by cartilage up to the age of puberty, but fuse thereafter to form a single bone. The lines of fusion can be seen on the anterior aspect of the bone.

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The manubriosternal joint is a symphysis. The xiphoid process is cartilaginous in children, but undergoes ossification in the adult. After this happens the xiphisternal joint is said to be a symphysis. However, unlike a typical symphysis the joint disappears in old age and the xiphoid process and the body of the sternum become united Fig. 5.2. Attachments on the anterior aspect of by bone. The junction of the first costal the sternum. cartilage with the manubrium is a synchondrosis. The other sternocostal joints usually have a joint cavity (i.e., they are synovial joints).

Attachments on the Sternum A. The muscles (and associated structures) attached to the anterior aspect of the sternum are as follows (Fig. 5.2) 1. The sternal head of the sternocleidomastoid arises from the upper part of the manubrium. 2. The pectoralis major arises from the corresponding half of the manubrium and of the body of the sternum. The origin extends onto the costal cartilages. 3. The rectus abdominis is inserted into the xiphoid process. The insertion extends to the 7th, 6th and 5th costal cartilages (in that order) along a horizontal line.

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4. The aponeurosis of the external oblique muscle of the abdomen, which covers the rectus abdominis, is attached just beyond the insertion of the latter. (The attachment of the aponeurosis is shown in green lines in figure 5.2). 5. The aponeuroses of the internal oblique muscle of the abdomen, and of the transversus abdominis, are attached to the sides of the xiphoid process. 6. The linea alba is attached to the apex (lower end) of the xiphoid process.

B. The muscles attached to the posterior surface of the sternum are as follows (Fig. 5.3) 1. The sternohyoid arises from the upper part of the posterior surface of the manubrium. The area extends onto the back of the clavicle. 2. The sternothyroid arises from the posterior surface of the manubrium, below the origin of the sternohyoid. The origin extends onto the first costal cartilage. 3. The sternocostalis arises from the lower one third of the posterior surface of the body, and of the xiphoid process (and also from the adjoining parts of the costal cartilages). 4. Sternal slips of the diaphragm arise from the back of the xiphoid process. Relations of the sternum The posterior aspect of the manubrium is related to the arch of the aorta and its branches, Fig. 5.3. Attachments on the posterior aspect and to the left brachiocephalic vein. Its lateral of the sternum. part is related to lungs and pleura. The body of the sternum is also related to lungs and pleura and to pericardium. The xiphoid process is related to the liver. Ossification of the Sternum The number of centres of ossification appearing in different segments of the sternum is variable: 1 to 3 in the manubrium, and one or two in each sternebra. The centres usually appear around the 5th month of fetal life. Ossification in the xiphoid process begins around the 3rd year or later. The sternebrae unite with each other between puberty and 25 years, the union starting inferiorly and proceeding upwards.

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The Ribs 3

TYPICAL RIBS The ribs are curved long bones that form the side walls of the thorax (Figs. 5.4, 5.5). There are twelve ribs on either side. They vary considerably in length: the seventh rib is the longest, those above and below it becoming progressively shorter. Adjacent ribs are separated by intercostal spaces. The ribs are attached behind to the thoracic vertebrae. The anterior ends of the upper seven ribs are attached to bars of cartilage (costal cartilages) through which they gain attachment to the sternum. They are called true ribs. The anterior ends of the eighth, ninth and tenth ribs also end in costal cartilages. These cartilages do not reach the sternum, but end by gaining attachment to the next higher costal cartilage. They are, therefore, called false ribs. The anterior ends of the eleventh and twelfth ribs have small pieces of cartilage attached to their ends: these ends are free and these ribs are, therefore, called floating ribs. At the posterior end of a typical rib we see a head, a neck and a tubercle. The head articulates partly with the superior costal facet on the body of the numerically corresponding vertebra; and partly with the inferior costal facet on the next higher vertebra (Fig. 4.7). It is also attached to the intervertebral disc. The part of the rib immediately lateral to the head is called the neck. It lies in front of the transverse process of the numerically corresponding vertebra.

Fig. 5.5. Section across the shaft of a typical rib

Fig. 5.4. A typical rib seen from below.

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It has a sharp upper border called the crest of the neck. Just lateral to the neck the posterior aspect of the rib presents an elevation called the tubercle. The tubercle has a medial articular part which bears a facet that articulates with the costal facet on the transverse process of the corresponding vertebra; and a lateral part that is rough for attachment of ligaments. The anterior end of the rib shows a cup shaped depression for attachment of the costal cartilage. The part of the rib between the anterior and posterior ends is called the shaft. It is curved like the letter ‘C’. The shaft is flat: it has inner and outer surfaces, and upper and lower borders. The upper border is rounded. The lower border is sharp. The inner surface is concave. Just above the lower border the inner surface shows a costal groove running along the length of the shaft. The external surface of the shaft is convex. A short distance lateral to the tubercle it is marked by a rough line. At this point the rib appears to be bent: this point is, therefore, called the angle. The shaft is also somewhat twisted along its long axis. As a result the external surface faces somewhat downwards in the posterior part and somewhat upwards in its anterior part.

Attachments and some relations of Typical Ribs 1. The head of each rib gives attachment to the fibrous capsule, the radiate ligament and the intra-articular ligament of the costovertebral joint. 2. The neck and tubercle give attachment to ligaments of the costotransverse joint. The superior costotransverse ligament is attached to the crest of the neck; the costotransverse ligament to the posterior surface of the neck; and the lateral costotransverse ligament to the rough nonarticular part of the tubercle. 3. The internal intercostal membrane is attached to the lower border and anterior surface of the neck of the rib. 4. Each external intercostal muscle is attached, superiorly, to the sharp lower border of the shaft; and inferiorly to the outer lip of the superior border (of the next lower rib). 5. The internal intercostal muscle is attached above to the floor of the costal groove; and below to the inner lip of the superior border (of the next lower rib). 6. The intercostalis intimus (innermost intercostal) is attached above to the upper border of the costal groove; and inferiorly to the inner lip of the superior border (of the next lower rib, along with the internal intercostal). 7. The external surfaces of typical ribs give attachment to a number of muscles, the exact attachments varying from rib to rib. The muscles include the serratus anterior, the pectoralis minor, the latissimus dorsi, the external oblique muscle of the abdomen, the levatores costae, and the iliocostalis cervicis (part of erector spinae). 8. The intercostal vessels and nerve (of an intercostal space) lie in relation to the costal groove, but are separated from the floor of the groove by the internal intercostal muscle.

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9. The sympathetic trunk descends vertically across the anterior aspect of the heads of lower ribs. 10. The internal surfaces of the ribs are covered by costal pleura.

3 ATYPICAL RIBS The First Rib The first rib (Fig. 5.6) can be distinguished by its small size, and by the fact that its shaft is broad and flat having upper and lower surfaces (instead of outer and inner), and inner and outer borders (instead of upper and lower). The head has a single facet as this rib articulates only with the first thoracic vertebra. The tubercle is prominent and coincides with the angle. The upper surface of the shaft has two shallow, but wide grooves (for the subclavian artery and vein). Near the inner border of the rib these two grooves are separated by a prominence called the scalene tubercle. The lower surface of the rib is smooth and does not have a costal groove.

Attachments and Relations of the first rib 1. The scalenus medius is inserted into a large rough area on the superior surface, behind the groove for the subclavian artery. 2. The scalenus anterior is inserted on the scalene tubercle, and the adjoining part of the upper surface of the rib.

Fig. 5.6. First rib seen from above.

Fig. 5.7. Attachments and relations of the first rib seen from above.

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3. The subclavius arises from the anterior end of the upper surface of the rib; and from the adjoining part of the first costal cartilage. 4. The first digitation of the serratus anterior arises from the outer border of the rib near the groove for the subclavian artery. 5. The outer border also gives attachment to intercostal muscles of the first space. 6. The costoclavicular ligament is attached to the rough area in front of the groove for the subclavian vein. 7. The inner border gives attachment to the suprapleural membrane. 8. The inferior surface of the rib is related to pleura and lung. 9. The groove for the subclavian artery lodges this artery, and also the lower trunk of the brachial plexus. The subclavian vein lies in its own groove. 10. Three important structures lie on the anterior aspect of the neck of the first rib. From medial to lateral side these are (a) the sympathetic trunk (cervicothoracic ganglion); (b) the superior intercostal artery (accompanied by the first posterior intercostal vein); and (c) the ventral ramus of the first thoracic nerve (which ascends across the first rib to join the brachial plexus).

The Second Rib The second rib can be distinguished from a typical rib by the fact that when placed on a flat surface the entire rib touches it. (In a typical rib the posterior end is lifted off the surface). The external surface is directed outwards and upwards (Fig. 5.8) (and not directly upwards as in the first rib). Near its middle it has a prominent rough area. The inner surface points medially and downwards. A short costal groove is present on its posterior part.

Fig. 5.8. Second rib (right) seen from above.

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Attachments and Relations (Fig. 5.9) 1. The upper and lower borders of the rib give attachment to intercostal muscles. 2. The scalenus posterior is inserted into the posterior part of the outer surface.

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3. The serratus anterior (first and second digitations) arises from the tubercle on the outer surface just behind the middle of the shaft. 4. A slip of the serratus posterior superior is attached just lateral to the tubercle. 5. The inner surface is related to lungs and pleura.

The Tenth, Eleventh and Twelfth Ribs

Fig. 5.9. Attachments on the superior aspect of the second rib.

These ribs can be distinguished from typical ribs as each of them bears only a single articular facet on the head. This is so because each of these ribs articulates only with the corresponding vertebra. In other respects the tenth rib is similar to a typical rib. The eleventh and twelfth ribs can be distinguished from the tenth rib as they are relatively short, have no necks or tubercles, and their ends are tapering (in contrast to the broad anterior ends of typical ribs). The eleventh rib can be distinguished from the twelfth as it has a slight angle, and a costal groove is discernible, but the twelfth rib has neither of these features.

Fig. 5.10. Twelfth rib (right) seen from the front. Note absence of neck, tubercle, angle and costal groove.

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Attachments on the twelfth rib (Figs. 5.11, 5.12) 1. Near the medial end the rib gives attachment to ligaments of the costovertebral joint and (posteriorly) to the lumbocostal ligament. 2. The medial part of the upper border gives attachment to intercostal muscles. 3. The diaphragm is attached to the lateral part of the upper border, and to the adjoining part of the anterior surface. 4. The quadratus lumborum is attached to the lower part of the medial half (or so) of the anterior surface.

Fig. 5.11. Attachments on the anterior aspect of the twelfth rib.

5. The layers of thoracolumbar fascia are attached as follows. (a) The anterior layer, to the anterior surface just above the attachment of the quadratus lumborum. (b) The middle layer to the lower border just below the attachment of the quadratus lumborum. (c) The posterior layer to the lower border, lateral to the attachment of the quadratus lumborum.

Fig. 5.12. Attachments on the posterior aspect of the twelfth rib.

6. The lateral arcuate ligament is attached to the lower border at the lateral end of the area for attachment of the quadratus lumborum. 7. The medial part of the posterior surface of the rib gives attachment to the lowest levator costae, and to part of the erector spinae. 8. The lateral part of the posterior surface gives attachment to slips for the latissimus dorsi, the external oblique muscle of the abdomen, and the serratus posterior inferior.

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Relationship of 12th rib to pleura The upper part of the medial half of the anterior surface (i.e., the area above that for the quadratus lumborum) is in contact with pleura (costodiaphragmatic recess).

3 Ossification of Ribs A typical rib has a primary centre that appears in the shaft during the second month of fetal life. Secondary centres appear around the age of puberty: one for the head, and one each for the articular and non-articular parts of the tubercle. The last mentioned centre is absent in the lower ribs. As the eleventh and twelfth ribs have no tubercles the relevant centres are absent in them.

The Costal Cartilages These are bars of hyaline cartilage (Fig. 2.4). A typical costal cartilage has medial and lateral ends, anterior and posterior surfaces, and upper and lower borders. The lateral end of each costal cartilage is attached to the anterior end of one rib. The medial ends of the upper seven costal cartilages are attached to the lateral margin of the sternum. The first costal cartilage is attached to the lateral margin of the manubrium sterni. The medial end of the second cartilage is attached partly to the manubrium and partly to the first sternebra. The 3rd, 4th and 5th cartilages gain attachment to the lateral edge of the sternum at the points of junction of sternebrae; the 6th on the fourth sternebra; and the 7th at the junction of the fourth sternebra and the xiphoid process. The medial ends of the 8th, 9th and 10th costal cartilages are connected to the next higher costal cartilage. The cartilages of the 11th and 12th ribs are small and are attached to the tips of the ribs. Their lateral ends are free. The joint between the first costal cartilage and the manubrium sterni is a synchondrosis. The 2nd to 7th costal cartilages are joined to the sternum thorough synovial joints. The junctions of the 8th, 9th and 10th cartilages with the next higher cartilage are also marked by the presence of synovial joints.

Attachments and Relations of Costal Cartilages 1. The superior and inferior borders give attachment to the internal intercostal muscles (internally) and to the external intercostal membranes (externally).

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2. The anterior surfaces of the first six or seven cartilages give origin to the pectoralis major. The 5th, 6th and 7th cartilages receive the insertion of the rectus abdominis. The 7th, 8th and 9th cartilages give attachment to the aponeurosis of the internal oblique muscle of the abdomen. 3. The posterior surfaces of the 2nd to 6th cartilages give attachment to the sternocostalis; and the 7th to 12th give origin to the transversus abdominis. 4. The first costal cartilage gives origin to the subclavius (anteriorly) and gives origin (posteriorly) to part of the sternothyroid. The upper surface of the cartilage also gives attachment to the costoclavicular ligament, and to the articular disc of the sternoclavicular joint.

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The Skull as a whole

General Review of the Skull The skull consists of a large number of bones. The purpose of this section is to make the student familiar with their names as a preliminary to further study. The bone forming the lower jaw is called the mandible (Fig. 6.1). The other bones of the skull are firmly united to one another at joints called sutures: these bones collectively form the cranium. (Cranium = skull minus mandible). The cranium consists of two main parts. Its upper and posterior part contains a large cranial cavity in which the brain lies. Anteriorly, and inferiorly, the cranium forms the skeleton of the face including the walls of the orbits (in which the eyeballs lie), the cavity of the nose, and the upper part of the cavity of the mouth. The upper dome-like part of the skull is called the vault or skull cap. It forms the upper, lateral, anterior and posterior walls of the cranial cavity. Note that its anterior wall forms the forehead. The part of the skull forming the floor of the cranial cavity is called the base.

Fig. 6.1 Some features of the skull as seen from the lateral side.

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With these preliminary remarks we can proceed to identify the individual bones of the skull. Looking at the skull from above (Fig. 6.2) we see four bones. The bone forming the anterior part of the vault is the frontal bone. The greater part of the roof and side walls of the cranial cavity are formed by the right and left parietal bones. The two parietal bones meet in the midline at the sagittal suture. Their anterior margins join the frontal bone at the coronal suture which runs transversely across the vault. The posterior part of the vault is formed by the occipital bone which is better seen when the skull is viewed from behind (Fig. 6.3). The suture joining the occipital bone to the parietal bones is shaped like the Greek letter ‘lambda’ (which is like an inverted ‘Y’). It is, therefore, called the lambdoid suture. Lateral to the occipital bone we see a part of the temporal bone (which is better seen when the skull is viewed from the lateral side)(Fig. 6.5).

Fig. 6.2. Some features of the skull as seen from above. For details see figure. 6.12.

When the skull is viewed from the front (Fig. 6.4) the most conspicuous features are the jaws which bear the teeth. The bone forming the lower jaw is called the mandible. The upper jaw is formed by the right and left maxillae. The region of the forehead is formed by the frontal bone. The prominence of the cheek is formed by the zygomatic bone. Three large openings can be seen. A median nasal aperture is present between the two maxillae: it leads into the nasal cavities. In Fig. 6.3. Some features of the skull as seen the depth of the aperture we can make out from behind. For details see figure 6.13. parts of three bones. These are the ethmoid, the inferior nasal concha, and the vomer. Above and lateral to the nasal aperture we see two large cavities, the right and left orbits, in which the eyeballs lie. The walls of the orbits receive contributions from the frontal, zygomatic, and ethmoid bones, from the maxilla, and from two bones not mentioned so far. One of these is a small bone, the lacrimal. The other is the sphenoid. The sphenoid is a large unpaired bone present in the base of the skull, and only a small part of it is seen in each orbit. A part of the sphenoid called the greater wing is also seen on the lateral

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Fig. 6.4. Bones of the skull that can be seen from the front. For details see 3 figure 6.8.

Fig. 6.5. Lateral view of the skull showing the position of individual bones. For further details see figures 6.14 to 6.17.

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surface of the skull. Lying in the area between the two orbits we see the right and left nasal bones. They lie just above the nasal aperture. The bones to be seen when the skull is viewed from the lateral side are shown in figure 6.5. Many of these have already been seen from the front, from above, or from behind. These include the frontal, parietal, and occipital bones (in the vault), and the ethmoid, lacrimal, nasal and zygomatic bones (in the facial region). The maxilla, the mandible, and the greater wing of the sphenoid are also seen. Below the parietal bone the lateral wall of the cranium is formed by the squamous part of the temporal bone. Lower down the mastoid part of the same bone lies in relation to the base of skull. The temporal bone gives off a process that joins (a process of) the zygomatic bone to form the zygomatic arch. When the skull is viewed from below (Fig. 6.6) we see parts of several bones already identified. These are the maxilla (shaded orange), the sphenoid (violet), the temporal (green) and the occipital bone (blue). We also see parts of the zygomatic bone and of the vomer; and the palatine bone which is seen for the first time. The maxillae bear the upper teeth. Lateral to the teeth a part of the maxilla is seen articulating with the zygomatic bone. Medial to the teeth the maxilla forms the anterior part of the bony palate. The posterior part of the palate is formed by the right and left palatine bones. Above the posterior edge of the palate we see the posterior openings of the right and left nasal cavities which are separated by the vomer. Part of the vomer has been seen on the front of the skull through the anterior nasal aperture. Behind the vomer we see the sphenoid which is an unpaired bone. It has a median part, the body. On either side of the body there is a greater wing (which is seen partly on the base of the skull and partly on the lateral wall: figure 6.5). Posteriorly, the body of the sphenoid is continuous with the basilar part of the occipital bone. Just behind the basilar part, the occipital bone has a large foramen, the foramen magnum through which the cranial cavity communicates with the vertebral canal. Posterior to the foramen magnum the occipital bone forms a large part of the base of the skull. The lateral part of the base of the skull is formed by the temporal bone which is wedged in between the sphenoid and occipital bones. It consists of a medial petrous (= stone like) part, a posterolateral mastoid part, and an anterolateral squamous part that is seen mainly on the lateral wall of the skull. The temporal bone gives off a process that joins the zygomatic bone to form the zygomatic arch. (Some other parts of the temporal bone will be identified later).

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Fig. 6.6. Some features of the skull as seen from below. For details see figures 6.21, 6.25 and 6.26.

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When the top of the skull (skull cap) is removed by a transverse cut we can view the floor of the cranial cavity (Fig. 6.7). It is seen to be divided into three depressions called the cranial fossae: anterior, middle (shaded with dots), and posterior. The floor of the anterior cranial fossa is formed mainly by the frontal bone, but near the midline, anteriorly, a small part is formed by the ethmoid. This bone lies mainly in the wall of the nasal cavity. A part of it has

Fig. 6.7. Bones of the skull as seen in the floor of the cranial cavity. The skull is viewed from above after removing the skull cap. Also see figures 6.28 and 6.30.

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been seen in the wall of the orbit, and another part through the anterior nasal aperture. More posteriorly the median part of the floor of the anterior fossa is formed by a part of the body of the sphenoid; and the lateral parts by the lesser wings of the sphenoid. The floor of each half of the anterior cranial fossa has a sharp posterior margin that separates 3 of it from the middle cranial fossa. The medial part of the margin is formed by the lesser wing the sphenoid, and its lateral part by the frontal bone. The floor of the middle cranial fossa is narrow (antero-posteriorly) in its median part, and broad laterally. The narrow median part is formed by the body of the sphenoid. The broad lateral part (which is also much deeper) is formed by the greater wing of the sphenoid, the squamous part of the temporal bone, and by the anterior surface of the petrous part of the same bone. The greater part of the floor of the posterior cranial fossa is formed by the occipital bone. The foramen magnum is seen in the deepest part of the fossa. The anterolateral part of the floor is formed by the posterior surface of the petrous temporal bone. The various bones to be seen on different aspects of the skull have been identified. We will now proceed to undertake a more detailed study of the skull as seen from various aspects.

The Skull as seen from the Front The bones seen when the skull is viewed from the front have already been identified, and the presence of the orbits and the anterior nasal aperture noted. We shall now consider further details (Fig. 6.8). The orbits and the mandible will be considered separately.

Articulations Lateral to the orbit the frontal bone ends in the zygomatic process which joins the frontal process of the zygomatic bone at the frontozygomatic suture. The nasal part of the frontal bone projects downwards between the two orbits. On either side of the midline it meets the frontal process of the maxilla at the frontomaxillary suture, and the nasal bone at the frontonasal suture. The nasal bones join each other at the internasal suture, and the frontal process of the maxilla at the nasomaxillary suture. Below the nasal aperture the right and left maxillae meet at the intermaxillary suture. Laterally, the maxilla has a prominent zygomatic process which articulates with the maxillary process of the zygomatic bone at the zygomaticomaxillary suture.

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Fig. 6. 8. Some details of features of the skull as seen from the front. Compare with figure 6.4. For details within the orbit see figure 6.11.

Other Named Features The surface of the frontal bone seen from the front is called the external surface. About 3 cm above the orbit it is somewhat more convex than elsewhere: this area is called the frontal tuber or frontal eminence. Just above the medial part of the orbit there is a raised ridge called the superciliary arch. The arches of the two sides meet in the midline at the glabella. The point where the frontonasal and internasal sutures meet is called the nasion. The zygomatic process of the frontal bone has a sharp lateral edge. When traced upwards it is continued as a ridge which is continuous posteriorly with the temporal lines. The ridge separates the external surface of the frontal bone from the temporal surface (which is better seen from the lateral side: figure 6.14). The features to be seen on the maxilla are as follows. The frontal process is marked by a sharp vertical ridge called the anterior lacrimal crest. This crest forms part of the medial margin of

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the orbit. The part of the frontal process behind the crest takes part in forming the lacrimal groove. (Also see figure 6.11). In the lower part of the nasal aperture, in the midline, the maxillae show a sharp forward projection called the anterior nasal spine. The part of the maxilla that bears the teeth is called the alveolar process. Each maxilla bears eight teeth. Beginning from the midline there are two incisors, one canine, two premolars and three molars. Just above the 3 canine tooth the maxilla shows a vertical elevation produced by the root of this tooth: this is the canine eminence. Medial to this eminence and above the incisor teeth there is a depression called the incisive fossa; and lateral to it there is another depression, the canine fossa.

Foramina At the junction of the medial one-third and the lateral two-thirds of the upper margin of the orbit we see the supraorbital notch which is sometimes converted into a foramen (Fig. 6.8). Medial to it a smaller frontal notch (or foramen) is often seen. On the lateral surface of the zygomatic bone we see the zygomatico-facial foramen which is sometimes double. About a centimeter below the inferior margin of the orbit there is a large infraorbital foramen on the anterior surface of the maxilla.

The Anterior Nasal Aperture The anterior nasal aperture is a pear shaped opening (Fig. 6.8). On either side its margin is formed mainly by the nasal notch of the maxilla. Its upper part is bounded by the lower borders of the nasal bones. In the depth of the aperture we can see the nasal septum separating the right and left nasal cavities. Its upper part is formed by a part of the ethmoid bone called the perpendicular plate and its lower part by the vomer. Lateral to the septum we see two curved plates of bone projecting into each nasal cavity from the lateral side. These are the middle and inferior nasal conchae. The middle concha is a part of the ethmoid bone while the Fig. 6.9. Schematic coronal section through the orbit and nasal cavity to show the bones related to them.

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Fig. 6.10. Attachments to the anterior aspect of the skull.

inferior concha is an independent bone that is attached to the maxilla. Some of the features mentioned above can be better visualized when we see a coronal section through the region of the nasal cavity and the orbit (Fig. 6.9). In particular, note the orientation of the ethmoid bone in relation to these cavities, and to the floor of the anterior cranial fossa.

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Attachments on the anterior aspect of the skull 1. The orbital part of the orbicularis oculi muscle arises from the nasal part of the frontal bone, and from the frontal process of the maxilla. The lacrimal part of the orbicularis oculi arises from the part of the lacrimal bone behind the lacrimal groove (Fig. 6.10).

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2. The corrugator supercilii arises from the medial end of the superciliary arch. 3. The zygomaticus major arises from the lateral surface of the zygomatic bone in front of the zygomatico-temporal suture. 4. The zygomaticus minor arises from the lateral surface of the zygomatic bone just behind the zygomatico-maxillary suture. 5. The levator labii superioris arises from the lower margin of the orbit, partly from the maxilla and partly from the zygomatic bone. 6. The levator anguli oris arises from the canine fossa of the maxilla below the infraorbital foramen. 7. The levator labii superioris alaeque nasi arises from the frontal process of the maxilla. 8. The procerus arises from the lower part of the nasal bone. 9. The nasalis has two parts. The transverse part arises from the maxilla just lateral to the nasal notch; and the alar part from the maxilla below and medial to the transverse part. 10. The depressor septi arises from the maxilla just above the central incisor tooth. 11. The incisivus labii superioris arises from the maxilla above the lateral incisor tooth. In figure 6.10 we also see parts of the attachments of the temporalis, the masseter and the buccinator. These are better seen from the lateral side.

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The Orbit Orbital Margins The upper margin of the orbit is formed by the frontal bone (Fig. 6.1). The lateral margin is formed mainly by the zygomatic bone: its upper part is formed by the zygomatic process of the frontal bone. The inferior margin is formed in its lateral part by the zygomatic bone, and in its medial part by the maxilla. The medial margin is formed mainly by the frontal process of the maxilla: its upper part is formed by the nasal part of the frontal bone.

Walls of the Orbit Each orbit is shaped like a pyramid. The orbital opening represents the base of the pyramid, while the apex lies at the posterior end. The orbit has a roof, a floor, a medial wall and a lateral wall; but these are not sharply marked off from one another.

Fig. 6.11. The orbit and surrounding structures. The figure is schematic to the extent that all features shown cannot be seen from one fixed angle of viewing.

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The roof is formed mainly by the orbital plate of the frontal bone. Posteriorly, a small part of it is formed by the lesser wing of the sphenoid. Note that these bones also form the floor of the anterior cranial fossa. The anterolateral part of the roof has a depression called the lacrimal fossa. Close to the orbital margin, at the junction of the roof and medial wall, there is a small depression called the trochlear fossa.

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The floor is formed mainly by the maxilla (This part of the maxilla is its orbital surface). The anterolateral part of the floor is formed by the zygomatic bone. Posteromedially, a small part of the floor is formed by a part of the palatine bone (called the orbital process). The lateral wall is formed, in its anterior part by the zygomatic bone, and in its posterior part by the greater wing of the sphenoid. The medial wall is formed mainly by the orbital plate of the ethmoid. Posterior to the ethmoid a small part of this wall is formed by the body of the sphenoid. Anterior to the ethmoid the wall is formed by the lacrimal bone, and still further anteriorly by the frontal process of the maxilla. The region of the medial wall formed by the lacrimal bone and by the maxilla shows a deep lacrimal groove (for the lacrimal sac). The groove is bounded anteriorly by the anterior lacrimal crest on the frontal process of the maxilla; and posteriorly by the crest of the lacrimal bone (which is a sharp vertical ridge). The suture joining the maxilla and the lacrimal bone runs vertically in the floor of the lacrimal groove. The groove is continuous, inferiorly, with the nasolacrimal canal, the lower end of which opens into the nasal cavity.

Apertures in the Orbit The superior orbital fissure is a prominent cleft that separates the posterior parts of the roof and lateral wall (Fig. 6.11). It is bounded above and medially by the lesser wing of the sphenoid; and below and laterally by the greater wing. Medial to it, at the apex of the orbit, there is the opening of the optic canal. This canal lies between the body of the sphenoid, and its lesser wing. The inferior orbital fissure intervenes between the posterior parts of the floor and the lateral wall of the orbit. It is bounded above and laterally by the greater wing of the sphenoid, and below and medially by the orbital surface of the maxilla. The fissure is continuous anteriorly with the infraorbital groove on the maxilla. Anteriorly, the groove ends in a canal which passes through the bony substance of the maxilla to open on the surface through the infraorbital foramen. At the junction of the roof and the medial wall, on the suture separating the orbital plate of the ethmoid from the frontal bone, we see the anterior and posterior ethmoidal foramina. On the lateral wall there are two small foramina on the orbital surface of the zygomatic bone: they open into canals within the bone. The other end of one of these canals opens on the external surface of the zygomatic bone as the zygomaticofacial foramen; and that of the other canal opens on the temporal surface of the zygomatic bone as the zygomaticotemporal foramen (Fig. 6.18).

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The Skull as seen from Above The names of the bones, and of the sutures, that are seen when the skull is viewed from above have already been mentioned. Some additional features may now be noted (Fig. 6.12). The point where the coronal and sagittal sutures meet is called the bregma, while the point where the sagittal suture meets the lambdoid suture is called the lambda. In the fetal skull (and for a few months after birth) there are gaps in the bones of the skull in these situations, these being filled by membranes. These gaps are called the anterior and posterior fontanelles. Examination of the parietal bone shows that in one area (in its posterolateral part) it is more convex than at other places: this area is called the parietal tuber (or eminence). Near the posterior part of the sagittal suture each parietal bone has a parietal foramen (which may sometimes be absent). The temporal lines can be seen on the lateral part of the parietal and frontal bones.

Fig. 6.12. Features seen on the skull when viewed from above. Compare with figure 6.2.

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The Skull as seen from Behind 3 When the skull is viewed from behind we again see the parietal tuber, the parietal foramen, the temporal lines, the sagittal suture, the lambdoid suture and the lambda (Fig. 6.13) The outline of the lambdoid suture may be extremely complicated, and sometimes small pieces of bone are completely surrounded by parts of the suture: these are called sutural bones. Below the lambdoid suture we see the occipito-mastoid suture which unites the lower part of the lateral border of the occipital bone to the mastoid part of the temporal bone. We also see the parieto-mastoid suture that unites the posterior part of the parietal bone to the mastoid part of the temporal bone. The part of the occipital bone seen from behind is the squamous part. It can be subdivided into an upper triangular part which is smooth, and forms the posterior part of the vault of the skull; and a lower part which is rough and forms the posterior part of the base of the skull. At the junction of these two parts there is a prominent projection in the midline called the external occipital protuberance. Running laterally from the protuberance there are the prominent superior nuchal lines. A little above these lines we see the highest nuchal lines which are faint and not always present. Below the external occipital protuberance there is a median ridge, the external occipital crest. Running laterally from the crest there are the right and left inferior nuchal lines.

Fig. 6.13. Features seen on the skull when viewed from behind. Compare with figure 6.3.

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The Skull as seen from the Lateral side Articulations The lower margin of the frontal bone articulates with several bones forming the frontonasal, frontomaxillary, frontolacrimal, fronto-ethmoid and frontozygomatic sutures (Fig. 6.14). These have already been seen from the front. Behind the frontozygomatic suture the frontal bone articulates with the upper border of the greater wing of the sphenoid at the frontosphenoid suture. The posterior end of this suture meets the coronal suture. We have already seen that the anterior end of the parietal bone meets the posterior border of the frontal bone at the coronal suture. Other articulations of the parietal bone are as follows. Its anteroinferior angle joins the greater wing of the sphenoid at the parietosphenoid suture. Further back the inferior border articulates with the squamous and mastoid parts of the temporal

Fig. 6.14. Sutures seen on the lateral aspect of the skull.

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bone at the parietosquamous and parieto-mastoid sutures. The posterior border of the bone is joined to the occipital bone through the lambdoid suture. Each parietal bone articulates with the the parietal bone of the opposite side through the sagittal suture. Near the anteroinferior angle of the parietal bone the sutures form an ‘H’ shaped arrangement. Four bones, the parietal, frontal, sphenoid (greater wing) and temporal (squamous part) come together and a small circle 3 drawn here encloses parts of all these bones. The area enclosed by the circle is called the pterion. (The centre of the pterion lies 4 cm above the zygomatic arch, and 3.5 cm behind the frontozygomatic suture. This fact is of surgical importance). We have already seen that the frontal process of the zygomatic bone joins the frontal bone, and that its maxillary process articulates with the maxilla. The bone also gives off a temporal process that runs backwards to join the zygomatic process of the temporal bone to form the zygomatic arch. Posteriorly, the frontal process of the zygomatic bone articulates with the anterior margin of the greater wing of the sphenoid (This suture is hidden from view by the frontal process: it is indicated in dotted line in Fig. 6.14). The temporal bone articulates with the parietal bone above; in front with the greater wing of the sphenoid, and through its zygomatic process with the zygomatic bone; and behind (through its mastoid part) with the occipital bone. Inferiorly, it bears a fossa for articulation with the head of the mandible to form the temporomandibular joint. The occipital bone articulates with the two parietal bones at the lambdoid suture. Lower down it articulates with the mastoid part of the temporal bone. The posterior border of the maxilla is joined to a part of the sphenoid bone called the pterygoid process, and to a small part of the palatine bone called the pyramidal process.

Foramina The parietal foramen and the zygomaticofacial foramen have already been identified. The zygomatico-temporal foramen is present on the temporal surface of the zygomatic bone (Fig. 6.18), and the mastoid foramen is situated on or near the occipitomastoid suture.

Other Named Features Note the following in figure 6.15. The lateral side of the vault of the skull is marked by a prominent curved ridge called the temporal line. This line starts anteriorly as a continuation of the sharp lateral edge of the zygomatic process of the frontal bone, and curving backwards it crosses the coronal suture. It then runs backwards across the parietal bone. Anteriorly a single ridge is seen, but posteriorly it is usually possible to make out two lines, superior and inferior. The superior line fades away on the posteroinferior part of the parietal bone. The inferior line curves forwards on to the temporal bone to become continuous with a ridge called the supramastoid crest. This crest separates the squamous and mastoid parts of the temporal

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Fig. 6.15. Some features seen on the lateral aspect of the skull. Also see figures. 6.1, 6.5, 6.14, 6.16 and 6.17.

bone, and is continuous anteriorly with the posterior root of the zygomatic process (see below). Just below this root we see an aperture leading into a bony tube called the external acoustic meatus. This meatus forms part of the external ear. The region between the temporal lines (above) and the zygomatic arch (below) is called the temporal fossa. In its floor we see parts of the frontal and parietal bones; of the squamous part of the temporal bone; and of the greater wing of the sphenoid bone. The anterior wall of the fossa (Fig. 6.18) is formed mainly by the temporal surface of the zygomatic bone. It also receives contributions from the greater wing of the sphenoid, and from the frontal bone. The mastoid part of the temporal bone lies behind the external acoustic meatus. In the young it is separated from the squamous part by the squamomastoid suture. Remnants of this suture may be visible in the adult. We have noted that the mastoid part of the temporal bone articulates with the parietal bone at the parietomastoid suture, and with the occipital bone at the occipitomastoid suture. The point at which these two sutures meet is called the asterion. Just behind the external acoustic meatus the mastoid part of the temporal bone shows a large downward projection called the mastoid process (Mastoid = like the breast). The styloid process

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Fig. 6.16. Additional features seen on the lateral aspect of the skull. Also see figures 6.1, 6.5, 6.14, 6.15 and 6.17.

(Styloid = needle like) is also a part of the temporal bone. It projects downwards and forwards from the inferior aspect of the bone. A number of additional features, located in the region of the zygomatic arch, are shown in figure 6.16. Note the following. The anterior part of the zygomatic arch is formed by the temporal process of the zygomatic bone. The posterior part of the arch is formed by the zygomatic process of the temporal bone. At its posterior end the zygomatic process of the temporal bone divides into anterior and posterior roots. The posterior root passes backwards along the lateral margin of the mandibular fossa, and then above the external acoustic meatus to become continuous with the supramastoid crest. The anterior root of the zygomatic process passes medially in front of the mandibular fossa. Two projections are seen in relation to the roots of the zygomatic process. At the junction of the anterior root with the process (i.e., just in front of the mandibular fossa) there is the tubercle of the root of the zygoma. The other projection is seen just behind the mandibular fossa: it is called the postglenoid tubercle.

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The bone around the opening of the external acoustic meatus is rough and serves to give attachment to the cartilaginous part of the meatus. Part of this area which forms the anterior margin, the inferior margin and the lower part of the posterior margin of the meatus belongs to the tympanic part of the temporal bone, also called the tympanic plate. Posteriorly, the tympanic part joins the mastoid part of the bone. The tympanic plate has a broad anterior surface which lies behind the mandibular fossa (which is formed by the squamous part of the temporal bone). The two are separated by the squamotympanic fissure. Just above and behind the external acoustic meatus there is an area called the suprameatal triangle. Its upper border is formed by the supramastoid crest. Its anteroinferior border is formed by the posterosuperior part of the external acoustic meatus. Its posterior border is an imaginary vertical line touching the posterior margin of the meatus. The importance of the triangle is that an important cavity, the mastoid antrum, lies deep to it in the substance of the petrous part of the temporal bone. The triangle itself is, however, formed by bone belonging to the squamous part of the temporal bone. Some features on the lateral side of the skull are obscured from view by the zygomatic arch and can be seen when the arch is cut away (Fig. 6.17). The temporal surface of the greater wing of the sphenoid has been seen in the floor of the temporal fossa. Inferiorly, this surface ends in

Fig. 6.17. Some details seen on the lateral aspect of the skull after removing the zygomatic arch.

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a sharp ridge called the infratemporal crest. Medial to the crest we see the infratemporal surface of the greater wing: this surface faces downwards. Further medially, we see another part of the sphenoid called the pterygoid process. This process projects downwards from the junction of the body and the greater wing. When viewed 3 from behind (Fig. 6.18) the process is seen to be made up of medial and lateral pterygoid plates that are free posteriorly, but meet anteriorly to enclose the pterygoid fossa. When viewed from the side (Fig. 6.17) we see the surface of the lateral pterygoid plate. Below and medial to the mandibular fossa we see another projection from the sphenoid called the spine. The irregular space lying lateral to the pterygoid process is called the infratemporal fossa. Its roof is formed mainly by the infratemporal surface of the greater wing of the sphenoid, with a small contribution from the squamous temporal. More laterally the fossa com-municates with the temporal fossa through the gap between the zygomatic arch and the side of the skull. The anterior wall of the infratemporal fossa is formed by the posterior surface of the maxilla (Fig. 6.18). The lowest part of this surface (which corresponds to the posterior end of the alveolar process) forms a projection called the maxillary tuberosity. The medial wall is formed by the pterygoid process, but in its lower part it is formed by a small part of the palatine bone called the pyramidal process. The anterior and medial walls of the infratemporal fossa meet below, but they are separated in the upper part by the pterygo-maxillary fissure. The fissure is continuous above with the inferior orbital fissure. The pterygomaxillary fissure leads into a space called the pterygo-palatine fossa which is described below.

Fig. 6.18. Anterior wall of temporal and infratemporal fossae seen from behind. The zygomatic process of the temporal bone has been removed, and a coronal section cut through the middle cranial fossa

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Fig. 6.19. Scheme to show the walls of the pterygopalatine fossa.

The Pterygopalatine fossa The walls of the pterygopalatine fossa are difficult to see. They are shown somewhat schematically in figure 6.19. The fossa has an anterior wall formed by the posterior surface of the maxilla; a posterior wall formed by the root of the pterygoid process; and a medial wall formed mainly by a part of the palatine bone (called the perpendicular plate) which separates the fossa from the nasal cavity. The uppermost part of the medial wall is formed by the body of the sphenoid bone. Laterally, the pterygopalatine fossa opens into the infratemporal fossa through the pterygomaxillary fissure. Above, the fossa communicates with the orbit through the inferior orbital fissure. The posterior wall of the fossa presents three openings. The upper and largest of these is the anterior end of the foramen rotundum (the other end of which opens into the middle cranial fossa). Below this there is the opening of the pterygoid canal. (The posterior end of this canal opens on the anterior wall of the foramen lacerum). Still lower down on the posterior wall there is the opening of the palatinovaginal canal. The medial wall of the fossa shows a large sphenopalatine foramen through which the fossa communicates with the nasal cavity. Inferiorly, the fossa is closed on the surface by meeting of the maxilla and the pterygoid process, but at a deeper plane there is an opening in the floor of the fossa which leads into the greater palatine canal (which opens inferiorly on the posterior part of the palate).

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Attachments on the Skull seen from the Lateral side 1. In the anterior part of the skull we see the attachments of several muscles of the face. These have already been described (Fig. 6.20). 2. The masseter arises from the zygomatic arch (lower border and deep surface).

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3. The buccinator arises from the lateral aspect of the maxilla (a little above the three molar teeth). Note that this muscle also arises from the mandible. 4. The lateral pterygoid arises by two heads. The lower head arises from the lateral surface of the lateral pterygoid plate. The upper head arises from the infratemporal surface and crest of the greater wing of the sphenoid bone.

Fig. 6.20. Attachments on the skull, seen from the lateral side.

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5. The superficial slip of the medial pterygoid muscle arises from the lateral aspect of the pyramidal process of the palatine bone and from the maxillary tuberosity (The main part of the muscle arises from the medial surface of the lateral pterygoid plate). 6. The temporalis arises from the whole of the temporal fossa. The area of origin is bounded above by the temporal line and below by the zygomatic arch. It includes parts of the frontal, parietal, and squamous temporal bones; and of the greater wing of the sphenoid bone. 7. The sternocleidomastoid muscle is inserted into the lateral half of the superior nuchal line; and into the lateral surface of the mastoid process (from its apex to its superior border). 8. The trapezius arises from the medial one third of the superior nuchal line, and from the external occipital protuberance (The attachment is better seen from below). 9. The occipitalis (or occipital belly of the occipitofrontalis) arises from the lateral part of the highest nuchal line and from the mastoid process. 10. The splenius capitis is inserted into the mastoid process and into the occipital bone just below the lateral one-third of the superior nuchal line (deep to the sternocleidomastoid). 11. The longissimus capitis is inserted into the mastoid process deep to the splenius capitis.

Fig. 6.21. Anterior part of the skull seen from below.

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12. The styloid process gives attachment to the following: (a) The stylohyoid muscle arises from its posterior aspect. (b) The styloglossus muscle arises from its anterior aspect near the tip. (c) The stylopharyngeus muscle arises from its medial aspect. (d) The stylohyoid ligament is attached to its tip. (e) The stylomandibular ligament it attached to its lateral side.

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The Skull as seen from Below The base of the skull presents a very large number of named features. The various bones that make up the base have been identified (Fig. 6.6). We shall now examine the features to be seen on each of these bones when the skull is viewed from below. A. Note the following in figure 6.21. In the anterior part of the skull we see the inferior aspect of the right and left maxillae. The alveolar process of the maxilla projects downwards and provides attachment to the upper teeth. The posterior end of each alveolar process forms a backward projection called the maxillary tuberosity. Within the concavity of the alveolar arch (i.e. the arch formed by the alveolar process) we see the bony palate which separates the nasal cavities (above) from the cavity of the mouth (below). The anterior part of the palate is formed by the palatal processes of the maxillae. The right and left processes meet in the midline at the intermaxillary suture. Overlying the anterior part of this suture there is a depression, the incisive fossa. On the side walls of this fossa we can see the lateral incisive foramina. In some skulls instead of the lateral incisive foramina there may be two median incisive foramina — anterior and posterior. The part of the alveolar process bearing the incisor teeth, and including the adjoining part of the palate is called the premaxilla. In the young a suture may be seen separating the premaxilla from the rest of the maxilla. Lateral to the alveolar arch we see the inferior aspect of the zygomatic process of the maxilla as it passes laterally to meet the zygomatic bone. We also see the posterior surface of the maxilla which is separated (posterolaterally) from the greater wing of the sphenoid by the inferior orbital fissure. The posterior part of the palate is formed by the palatine bones. This part of each palatine bone is called the horizontal plate. The right and left palatine bones articulate with each other at the interpalatine suture. They articulate with the posterior margins of the palatal processes of the maxillae at the palatomaxillary sutures. The posterior borders of the horizontal plates of the palatine bones are free and form the posterior margin of the hard palate. In the midline the margin projects backwards beyond the rest of it forming the posterior nasal spine. A little in front of the posterior border we see a curved ridge called the palatine crest. The posterolateral part of the horizontal plate gives off a projection called the pyramidal process. This process

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projects backwards and laterally. We have already seen that it occupies the gap between the lower ends of the medial and lateral pterygoid plates. It has been viewed from the lateral side in figure 6.17, and from behind in figure 6.18; and it is now seen from below. The part of the palate formed by the palatine bone shows the greater and lesser palatine foramina. The greater palatine foramen lies on the most lateral part of the horizontal plate, just medial to the last molar tooth. It is the lower opening of the canal of the same name already seen in relation to the floor of the pterygopalatine fossa. Anteriorly, the foramen is continuous with a vascular groove that runs forwards along the lateral margin of the palate. The lesser palatine foramina, usually two, are present on the pyramidal process just behind the greater palatine foramen. Just above the posterior margin of the hard palate there are two posterior nasal apertures. (Note that as the skull is being viewed from below the palate appears to form the roof of the aperture, but is really the floor). Each aperture is bounded, below, by the posterior edge of the horizontal plate of the palatine bone. The lateral wall of the aperture is formed by another part of the palatine bone which is called the perpendicular plate. As indicated by its name the perpendicular plate is placed at right angles to the horizontal plate. The posterior edge of the perpendicular plate is fused to the medial pterygoid plate of the sphenoid bone, the two together forming a flat plate of bone that forms the lateral wall of the region where the nose and pharynx meet. The perpendicular plate separates the nasal cavity from the pterygopalatine fossa. At this stage it is useful to recapitulate the various parts of the palatine bone. These are the horizontal and perpendicular plates, the pyramidal process, and the orbital process (which forms a small part of the floor of the orbit). A small part of the palatine bone, called the sphenoidal process has not been mentioned so far. It projects medially from the upper end of the perpendicular plate and takes part in forming the roof of the posterior nasal aperture (Fig. 6.22). (Also see below). The vomer is a flat plate of bone that forms part of the nasal septum. It has been seen through the anterior nasal aperture (Fig. 6.8). Now we see it separating the right and left posterior nasal

Fig. 6.22. Scheme to show the bones around the posterior nasal aperture.

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apertures (Fig. 6.21). Superiorly, the plate of bone forming the vomer divides into two alae that articulate with the inferior surface of the body of the sphenoid (Fig. 6.22). B. Note the following features to be seen on the sphenoid bone in figures 6.21 to 6.25. The sphenoid bone is large, extending across the entire width of the base of the skull and extending also onto the side wall of the vault. It is made up of several parts that have already been encountered. These are the body (which is median in position), the right and left greater and lesser wings, and the right and left pterygoid processes. When viewed from below the body of the sphenoid is seen in the roof of the posterior part of the nasal cavity and of the adjoining nasopharynx. The region is irregular and presents a number of plates and canals. Details of these are difficult to appreciate in the actual specimen. They are shown diagrammatically in figure 6.22. Projecting downwards from the body of the sphenoid there is a median ridge called the rostrum. The rostrum of the sphenoid bone fits into the gap between the alae of the vomer. Projecting medially from the root of the pterygoid process there is a horizontal vaginal plate which overlaps the lateral part of the ala. Projecting medially from the upper part of the perpendicular plate of the palatine bone there is its sphenoidal process which overlaps the (anterior part of the) vaginal plate. The palatovaginal canal is placed between these two plates. It runs forwards to open on the posterior wall of the pterygopalatine fossa. The vomerovaginal canal is not always present: when present it lies between the vaginal plate of the sphenoid and the ala of the vomer. It runs forwards to join the palatinovaginal canal. Posteriorly, the body of the sphenoid is directly continuous with the basilar part (or body) of the occipital bone.

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Fig. 6.23. Schematic coronal section to show relationship of the pterygoid process to the rest of the sphenoid bone.

Fig. 6.24. Schematic transverse sections to show the arrangement of the medial and lateral pterygoid plates at (A) upper, (B) middle , and (C) lower levels.

The pterygoid process has already been seen from the lateral aspect (Fig. 6.17). We have seen that it projects downwards from the junction of the body of the sphenoid with the greater wing, and that it consists of medial and lateral pterygoid plates. These plates meet anteriorly, but

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Fig. 6.25. Part of the base of the skull formed by the temporal and sphenoid bones. Some adjoining areas are also shown

posteriorly they are free. The space between them is called the pterygoid fossa. Anteriorly, the pterygoid process is fused to the posterior aspect of the maxilla in its middle part. Higher up it is separated from the maxilla by the pterygomaxillary fissure. In figure 6.24A note how the perpendicular plate of the palatine bone closes the pterygopalatine fossa medially, and at the same time meets the anterior margin of the medial pterygoid plate. In their lowest parts the pterygoid plates are separated by a gap (Fig. 6.23) which is filled by the pyramidal process of the palatine bone (Figs. 6.24C, 6.25). This process can be seen from behind forming the lower part of the floor of the pterygoid fossa (Fig. 6.18) and also from the lateral side, in the medial wall of the infratemporal fossa (Fig. 6.17). The medial pterygoid plate is directed backwards so that it has medial and lateral surfaces, and a free posterior border. The upper end of this border divides to enclose a triangular depression called the scaphoid fossa (Fig. 6.25). Medial to this fossa there is a small tubercle which projects into the foramen lacerum (see below). It hides from view the posterior opening of the pterygoid canal: the anterior end of this canal opens on the posterior wall of the pterygopalatine fossa.

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The lower end of the posterior border is prolonged downwards and laterally to form the pterygoid hamulus. The lateral pterygoid plate projects backwards and laterally. It has medial and lateral surfaces. At its upper end its lateral surface becomes continuous with the infratemporal surface of the 3 greater wing (Figs. 6.17, 6.23). The greater wing of the sphenoid (Fig. 6.25) has infratemporal and temporal surfaces that can be seen from below; and an orbital surface that has already been seen in the lateral wall of the orbit (Fig. 6.11). The temporal surface has been described earlier. The anterior margin of the infratemporal surface is separated from the maxilla by the inferior orbital fissure. Laterally, it is separated from the temporal surface by the infratemporal crest. The posterior margin of the lateral part of the infratemporal surface articulates with the infratemporal surface of the squamous part of the temporal bone. Medially, the infratemporal surface of the greater wing is continuous with the body of the sphenoid. Posteriorly, the greater wing meets the anterior margin of the petrous temporal bone.

Fig. 6.26. Posterior part of base of skull (formed by the temporal and occipital bones)

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Two important foramina are seen near the posterior border of the greater wing. The foramen ovale lies posterolateral to the upper end of the lateral pterygoid plate. Posterolateral to the foramen ovale there is a smaller round foramen called the foramen spinosum. It is so called because it lies just in front of a downward projection called the spine of the sphenoid. A third small foramen is sometimes seen medial to the foramen ovale. It is called the emissary sphenoidal foramen (Fig. 6.25, 6.32). Between the foramen ovale and the foramen spinosum another small foramen the canaliculus innominatus may be present . Posteromedial to these foramina, and to the spine of the sphenoid, the posterior margin of the greater wing forms the anterior wall of a prominent groove. The posterior wall of this groove is formed by the petrous temporal bone. The two bones meet in the floor of the groove which is meant for the cartilaginous part of the auditory tube. Traced laterally, the groove ends in relation to the opening of the bony part of the auditory tube.

C. Additional features on the temporal and occipital bones (Fig. 6.25, 6.26) In earlier pages we have seen that the temporal bone consists of squamous, petrous, mastoid and tympanic parts, and that the styloid process also belongs to it. Several landmarks that have been identified on the bone from the lateral aspect (Fig. 6.16) can be seen again from below. These are the zygomatic process, the tubercle of the root of the zygoma, the postglenoid tubercle, the mastoid process, the tympanic plate, the squamotympanic fissure, and the styloid process. We shall now examine some further details. The squamous part of the temporal bone has a temporal surface that has been seen from the lateral aspect: part of it can be seen from below. Inferior and medial to the temporal surface the squamous part has an infratemporal surface which takes part in forming the roof of the infratemporal fossa (along with the infratemporal surface of the greater wing of the sphenoid). Behind its infratemporal surface, the squamous part bears the mandibular fossa. This fossa is bounded anteriorly by a rounded eminence called the articular tubercle. The articular area for the mandible extends on to the tubercle. The tympanic plate separates the mandibular fossa from the external acoustic meatus. (The arrow in figure 6.25 points to the opening of the meatus which cannot be seen from below). The junction of the fossa (squamous part) with the tympanic plate is marked by the squamotympanic fissure. Projecting through the fissure we sometimes see the lower edge of a plate of bone called the tegmen tympani. The tegmen tympani belongs to the petrous part of the temporal bone. When present it divides the squamotympanic fissure into a petro-squamous part (anteriorly), and a petro-tympanic part (posteriorly). The posterior part of the tympanic plate partially surrounds the base of the styloid process and is fused with the mastoid part of the temporal bone. We have already seen that the plate has a rough lateral margin surrounding the opening of the external acoustic meatus. The petrous part of the temporal bone runs forwards and medially between the greater wing of the sphenoid (anterolaterally), and the occipital bone (posteromedially). Its apex is separated from the body of the sphenoid, the root of the pterygoid process, and the basilar part of the occipital bone by a very irregular aperture called the foramen lacerum. The inferior surface of

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the petrous temporal bone is marked by a large round opening. This is the lower opening of the carotid canal through which the internal carotid artery enters the cranial cavity. The canal passes medially, through the substance of the petrous temporal bone and opens into the posterior wall of the foramen lacerum. Behind the opening of the carotid canal there is another large depression, the jugular fossa. This fossa leads posteriorly into the jugular foramen which is 3 bounded posteriorly and below by the occipital bone, and opens into the posterior cranial fossa. In the mastoid part of the temporal bone we have already noted the presence of the mastoid process, and of the mastoid foramen. Medial to the mastoid process there is a deep mastoid notch. Near the anterior end of the notch, and just behind the styloid process we see the stylomastoid foramen. Medial to the mastoid notch the bone is grooved by the occipital artery. The greater part of the occipital bone is seen when the skull is viewed from below. The most conspicuous feature on it is the large foramen magnum through which the cranial cavity communicates with the vertebral canal. The part of the bone anterior to the foramen magnum is the basilar part. Anteriorly, the basilar part is directly continuous with the body of the sphenoid bone. These two bones are separated by a plate of cartilage in the young, but fuse with each other in the adult. (In figure 6.25 the position of this cartilage is shown in dotted line) A short distance in front of the foramen magnum the basilar part shows a small elevation in the midline called the pharyngeal tubercle. The parts of the occipital bone lateral to each side of the foramen magnum are its lateral (or condylar) parts. Here we see the prominent occipital condyles. The long axis of each condyle is directed forwards and medially, the condyle being markedly convex in this direction. Each condyle (right or left) articulates with the corresponding superior articular facet on the atlas vertebra to form an atlanto-occipital joint. There are two canals closely related to the occipital condyles. The hypoglossal (or anterior condylar) canal opens on the surface of the skull just above the lateral border of the anterior part of the condyle, and is hidden from view by the condyle. (It is, therefore, shown in dotted line). The canal runs backwards to open into the posterior cranial fossa. Behind the condyle there is a depression, the condylar fossa in which the opening of the posterior condylar canal is sometimes seen. The part of the occipital bone lateral to the condyle is called the jugular process. It forms the posterior (and inferior) wall of the jugular fossa and foramen. The jugular foramen passes backwards and medially from the fossa. It is often partially divided by projecting spicules of bone into anterior, middle and posterior parts. The position of two small foramina present in relation to the jugular fossa should be noted. One is present on the lateral wall of the fossa and is called the mastoid canaliculus. The other is present on the ridge of bone that separates the jugular fossa from the opening of the carotid canal: this is the canaliculus for the tympanic nerve (tympanic canaliculus). The part of the occipital bone behind the foramen magnum is the squamous part. It articulates with the mastoid part of the temporal bone at the occipitomastoid suture, on or near which we see the mastoid foramen. Posteriorly, the squamous part forms the posterior part of the vault of the skull and joins the right and left parietal bones at the lambdoid suture. Its external surface is marked by the external occipital protuberance; the external occipital crest; the inferior, superior

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and highest nuchal lines; and by numerous unnamed ridges that give it a rough surface for muscular attachments. The attachments on the base of the skull are described below.

Attachments on the Skull as seen from Below 1. The masseter arises from the lower border of the zygomatic arch (Fig. 6.27). 2. The upper head of the lateral pterygoid arises from the infratemporal surface and infratemporal crest of the greater wing of the sphenoid. The lower head of the muscle arises from the lateral surface of the lateral pterygoid plate. 3. The medial pterygoid arises from the medial surface of the lateral pterygoid plate and from the pyramidal process of the palatine bone. 4. The tensor palati arises from the scaphoid fossa, from the medial side of the spine of the sphenoid, and from the posterior margin of the greater wing of the sphenoid. It is inserted into the posterior edge of the palatine bone. 5. The tensor tympani arises from the greater wing of the sphenoid (and from the adjoining part of the wall of the auditory tube). 6. The levator palati arises from the inferior surface of the petrous temporal bone. 7. The musculus uvulae arises from the posterior edge of the hard palate near the midline (i.e., from the posterior nasal spine). 8. The posterior belly of the digastric muscle arises from the mastoid notch on the temporal bone. 9. The longus capitis is inserted into the inferior surface of the basilar part of the occipital bone. 10. The rectus capitis anterior is inserted into the occipital bone just in front of the condyle. 11. The rectus capitis lateralis is inserted into the inferior surface of the jugular process of the occipital bone. 12. The rectus capitis posterior major is inserted into the lateral part of the area between the inferior nuchal line and the foramen magnum. 13. The rectus capitis posterior minor is inserted into the medial part of the area between the inferior nuchal line and the foramen magnum.

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Fig. 6.27. Attachments on the skull seen from below.

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14. The semispinalis capitis is inserted into the medial part of the area between the superior and inferior nuchal lines. 15. The obliquus capitis superior is inserted into the lateral part of the area between the superior and inferior nuchal lines. 16. The trapezius arises from the medial one third of the superior nuchal line and from the external occipital protuberance. 17. Other muscles whose attachments are seen in figure 6.27 are the occipitalis, the sternocleidomastoid, the splenius capitis, and the longissimus capitis. 18. The pharyngeal tubercle (on the basilar part of the occipital bone) gives attachment to the uppermost fibres of the superior constrictor muscles of the pharynx. It also gives attachment to the upper end of a fibrous raphe that receives the insertion of lower fibres of these muscles. 19. The pterygomandibular ligament is attached to the tip of the pterygoid hamulus. 20. The pterygospinous ligament extends between the spine of the sphenoid and the upper part of the lateral pterygoid plate. 21. The sphenomandibular ligament is attached to the spine of the sphenoid. 22. The upper end of the ligamentum nuchae is attached to the external occipital protuberance, and to the external occipital crest. 23. The alar ligaments (of the dens) are attached to the occipital bone just medial to the condyles. 24. The anterior and posterior atlanto-occipital membranes are attached to corresponding margins of the foramen magnum.

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The Cranial Fossae 3 When the upper part of the vault of the skull is removed we can see the floor of the cranial cavity (or, in other words, the base of the skull as seen from above) (Figs. 6.28 to 6.30). We have seen that the floor is subdivided into anterior, middle and posterior cranial fossae. The bones to be seen have been identified. We shall now examine the fossae in greater detail. The floor of the anterior cranial fossa (Fig. 6.28) is formed mainly by the orbital plates (right and left) of the frontal bone. Anteriorly, the right and left halves of the frontal bone are separated by a median projection called the frontal crest. Just behind the crest there is a depression called the foramen caecum. Between the right and left orbital plates of the frontal bone there is a notch occupied by the cribriform plate of the ethmoid bone. This plate has numerous foramina. It also bears a median vertical projection called the crista galli which lies immediately behind the foramen caecum.

Fig. 6..28. Parts of the anterior and posterior cranial fossae seen from above. Compare with figure 6.7.

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The anterior and posterior ethmoidal canals (already seen on the medial wall of the orbit) open into the anterior cranial fossa near the lateral edge of the cribriform plate, but they are difficult to see. The posterior part of the floor of the anterior cranial fossa is formed by the sphenoid bone. In the median part it is formed by the anterior part of the superior surface of the body of the sphenoid: this region is called the jugum sphenoidale. Lateral to the jugum sphenoidale the floor is formed by the lesser wing of the sphenoid. The lesser wing also forms the sharp posterior edge of the floor of the anterior cranial fossa. The medial edge of each lesser wing projects backwards as the anterior clinoid process. The middle cranial fossa (Figs. 6.28 to 6.30) has a raised median part formed by the body of the sphenoid bone, and two large deep hollow areas on either side (Fig. 6.29). The features to be seen in relation to the body of the sphenoid are as follows. Immediately behind the jugum sphenoidale the body of the sphenoid is crossed by a transverse shallow groove that connects the two optic canals, and is called the sulcus chiasmaticus (even though the optic chiasma does not lie over the sulcus). Behind the sulcus the superior surface of the body of the sphenoid shows a median elevation, the tuberculum sellae; and behind the tuberculum there is a depression called the hypophyseal fossa. Posterior to the fossa there is a vertical plate of bone called the dorsum sellae. The deep hollow bounded anteriorly by the tuberculum sellae, and posteriorly by the dorsum sellae is called the sella turcica. The superolateral angles of the dorsum sellae are called the posterior clinoid processes. The sides of the body of the sphenoid slope downwards (Fig. 6.29) into the floor of the deep lateral part of the middle cranial fossa. In this situation each side of the body of the sphenoid is marked by a shallow carotid groove. Posteriorly, the groove becomes continuous with the foramen lacerum. Anteriorly, it turns upwards medial to the anterior clinoid process. On either side, the anterior wall of the middle cranial fossa is formed (Fig. 6.29) by the greater and lesser wings of the sphenoid. The lesser wings are attached to the sides of the body of the sphenoid by two roots: anterior (or upper), and posterior (or lower). The optic canal passes forwards and laterally between the body of the sphenoid and the two roots of the lesser wing. The greater and lesser wings are separated by the superior orbital fissure which leads into the orbit. Just below the medial end of the fissure, and just lateral to the carotid groove we see the foramen rotundum. We have already noted that this foramen opens anteriorly into the pterygopalatine fossa. The posterior wall of the middle cranial fossa (Fig. 6.30) is formed, on either side, by the anterior sloping surface of the petrous temporal bone. The apex of the bone is separated from the body of the sphenoid by the foramen lacerum already seen from below. A little above and lateral to the foramen the surface of the petrous temporal bone shows a shallow depression called the trigeminal

Fig. 6.29. Schematic diagram to show some features in the anterior wall of the middle cranial fossa.

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Fig. 6.30. Features to be seen in the floor of the middle and posterior cranial fossae. Compare with figure 6.7.

impression. Lateral to this impression we see two grooves running downwards and medially. The upper and more prominent groove begins at a minute aperture called the hiatus for the greater petrosal nerve. Below and lateral to it we have another groove which begins at the hiatus for the lesser petrosal nerve. More laterally, the anterior surface is marked by an elevation called the arcuate eminence. Lateral to the arcuate eminence the anterior surface of the petrous temporal bone is formed by a thin plate of bone that separates the middle cranial fossa from the cavities of the middle ear, the auditory tube and the mastoid antrum. This plate is called the tegmen tympani. It is the lower end of this plate which appears in the squamotympanic fissure.

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The floor of the deep lateral part of the middle cranial fossa is formed by the greater wing of the sphenoid, medially, and by the squamous part of the temporal bone, laterally. Near the posterior margin of the greater wing we see the foramen ovale, the foramen spinosum, and sometimes the emissary sphenoidal foramen, all of which have already been seen from below. The lateral wall of the middle cranial fossa is formed, anteriorly, by the greater wing of the sphenoid, and posteriorly by the squamous temporal bone. The anteroinferior angle of the parietal bone contributes to the most anterior part of the lateral wall (in the region of the pterion). A vascular groove (for the middle meningeal vessels) starts at the foramen spinosum and runs forwards on the floor. It divides into an anterior (or frontal) branch and a posterior (or parietal) branch. The frontal branch runs upwards and forwards to the region of the inner surface of the pterion: here the groove is often converted into a canal. It then runs upwards and backwards on the inner surface of the parietal bone. The parietal branch runs backwards first on the squamous temporal, and then on the parietal bone. The most prominent landmark in the posterior cranial fossa (Fig. 6.30) is the foramen magnum already seen from below. Anterior to the foramen magnum the wall of the fossa is formed by the basilar part of the occipital bone which is continuous above with the posterior surface of the body of the sphenoid: this area is called the clivus. The lateral margin of the basilar part of the occipital bone is separated from the petrous temporal bone by the petrooccipital fissure, which ends below in the jugular foramen. We have already noted that projections from the walls of the foramen partially divide it into anterior, middle and posterior parts. Between the jugular foramen, laterally, and the anterior part of the foramen magnum, medially, there is a rounded elevation called the jugular tubercle. In the interval between the jugular tubercle and the foramen magnum there is a fossa. The hypoglossal canal opens into this fossa. When present, the posterior condylar canal opens just lateral to the jugular tubercle immediately behind the jugular foramen. The lateral part of the anterior wall of the posterior cranial fossa is formed by the posterior surface of the petrous temporal bone. A little above the jugular foramen this surface presents the opening of the internal acoustic meatus. Posterolateral to this opening a slit in the bone leads into a canal called the aqueduct of the vestibule. The floor and lateral walls of the posterior cranial fossa are formed, posteriorly, by the squamous part of the occipital bone; and in the anterolateral part by the mastoid part of the temporal bone. The posteroinferior angle of the parietal bone makes a small contribution to the anterior part of the lateral wall. Behind the foramen magnum the two halves of the fossa are separated by a ridge called the internal occipital crest. Posteriorly, the crest ends in an elevation called the internal occipital protuberance. Running laterally from the protuberance, in the transverse plane, we see a prominent wide groove (transverse sulcus) in which the transverse sinus is lodged. The groove on the right side is generally more prominent than that on the left. The groove first lies on the occipital bone, and near its lateral (or anterior) end it crosses the posteroinferior angle of the parietal bone. It then runs downwards and medially with an Sshaped curve, deeply grooving the petrous and mastoid parts of the temporal bone to reach the jugular foramen. This S-shaped part of the groove is called the sigmoid sulcus. The terminal part of the groove lies on the occipital bone just behind the jugular foramen. The mastoid foramen (already seen on the external surface of the skull) opens into the part of the sigmoid sulcus formed by the mastoid temporal bone.

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FORAMINA OF THE SKULL We have seen that the bones of the skull show numerous foramina, small and large. In this section we shall consider the structures passing through these foramina. We will first list those foramina that give passage to very important structures like cranial nerves, large blood vessels 3 etc. This will be followed by a more complete listing of structures passing through individual foramina.

Most Important Foramina of the Skull 1. The lower end of the medulla oblongata passes through the foramen magnum to become continuous with the spinal cord. 2. The internal carotid artery enters the skull by passing through the carotid canal. 3. The junction of the upper end of the internal jugular vein with the sigmoid sinus lies in the jugular foramen. 4. Bundles of nerve fibres that constitute the olfactory nerve pass through minute apertures in the cribriform plate of the ethmoid bone. This plate intervenes between the nasal cavity and the anterior cranial fossa. 5, The optic nerve passes from the middle cranial fossa into the orbit through the optic canal. 6. The oculomotor, trochlear and abducent nerves enter the orbit through the superior orbital fissure. 7. The trigeminal nerve has three divisions each of which leaves the middle cranial fossa through a different foramen. The ophthalmic division enters the orbit through the superior orbital fissure. The maxillary division passes into the foramen rotundum, while the mandibular division passes through the foramen ovale to reach the infratemporal region. 8. The facial nerve leaves the posterior cranial fossa by passing into the internal acoustic meatus. After a complicated course through the petrous part of the temporal bone, it leaves the cranial cavity through the stylomastoid foramen. 9. The vestibulocochlear nerve leaves the posterior cranial fossa by passing through the internal acoustic meatus, to reach the internal ear which lies within the substance of the petrous part of the temporal bone. 10. The glossopharyngeal, vagus and accessory nerves leave the posterior cranial fossa through the jugular foramen, to enter the neck. 11. The hypoglossal nerve leaves the posterior cranial fossa through the hypoglossal canal.

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DETAILED LIST OF FORAMINA OF THE SKULL AND OF STRUCTURES PASSING THROUGH THEM

A. Foramina on the Anterior aspect of the Skull (Fig. 6.8) The supraorbital notch (or foramen), the infraorbital foramen, and the zygomatico-facial foramen transmit nerves and vessels of the same names.

B. Foramina in the Orbit (Figs. 6.11, 6.31) 1. The optic canal transmits the optic nerve (surrounded by meninges); and the ophthalmic artery. 2. The structures passing through the superior orbital fissure are as follows (Fig. 6.31). Through the upper (and lateral) part: (a) Trochlear nerve. (b) Frontal and lacrimal branches of the ophthalmic division of the trigeminal nerve. (c) Recurrent branch of the ophthalmic artery. (d) Superior ophthalmic vein. Through the middle part (within the tendinous ring): (a) Superior and inferior divisions of oculomotor nerve. (b) Nasociliary branch of ophthalmic division of the trigeminal nerve. (c) Abducent nerve. Through the lower (and medial) part: (a) Inferior ophthalmic vein. 3. The structures passing through the inferior orbital fissure are (Fig. 6.31): (a) Maxillary nerve. (b) Zygomatic nerve. (c) Infraorbital vessels. (d) Emissary veins connecting the inferior ophthalmic veins to the pterygoid plexus.

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Fig. 6.31. Structures passing through the optic canal, the superior orbital fissure, and the inferior orbital fissure.

4. The infraorbital groove and canal transmit the infraorbital nerve (continuation of maxillary nerve) and the infraorbital vessels. 5. The nasolacrimal canal transmits the nasolacrimal duct. 6. The lateral wall of the orbit has openings for the zygomaticotemporal and zygomaticofacial nerves and vessels. These structures pass through the thickness of the zygomatic bone. The zygomaticofacial nerve and vessels appear on the lateral surface of the bone through the zygomatico-facial foramen. The zygomatico-temporal nerves and vessels appear on the temporal surface of the bone (on the anterior wall of the temporal fossa) through the zygomaticotemporal foramen. 7. The medial wall of the orbit shows the openings of the anterior and posterior ethmoidal canals. The openings lie on the suture between the frontal and ethmoid bones. The canals pass through the interval between these bones to reach the floor of the anterior cranial fossa at the lateral edge of the cribriform plate. They transmit the anterior and posterior ethmoidal nerves and vessels.

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C. Foramina seen on the Lateral Side of the Skull 1. The zygomaticotemporal foramen has been mentioned above. 2. The terminal part of the maxillary artery enters the pterygomaxillary fissure. The maxillary nerve passes across the upper part of the fissure. 3. The sphenopalatine foramen (in the medial wall of the pterygopalatine fossa (Fig. 6.19) gives passage to the nasopalatine nerve and vessels. 4. The mastoid foramen is traversed by an emissary vein connecting the sigmoid sinus to occipital veins. 5. The parietal foramen is traversed by an emissary vein connecting the superior sagittal sinus to the veins of the scalp.

D. Foramina seen on the Base of the Skull Note that many of the foramina considered below are also seen in the floor of the cranial fossae. 1. The lateral incisive foramina are present in the lateral wall of the incisive fossa (Fig. 6.21). They lead into the incisive canals which transmit the terminal branches of the greater palatine vessels (from the palate to the floor of the nose); and of the nasopalatine nerves (from the nose to the palate). The right and left incisive foramina are sometimes replaced by anterior and posterior foramina; in that case the left nasopalatine nerve passes through the anterior foramen and the right through the posterior foramen. 2. The greater and lesser palatine foramina are seen on the posterior part of the palate (Fig. 6.21). They transmit nerves and vessels of the same names.

Fig. 6.32. Structures passing through the foramen ovale, and through smaller foramina near it. The lesser petrosal nerve sometimes passes through the canalis innominatus.

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3. The foramen ovale (Fig. 6.32) transmits the mandibular division of the trigeminal nerve, the accessory meningeal artery, and emissary veins connecting the cavernous sinus to the pterygoid venous plexus. When the canaliculus innominatus is not present the foramen ovale transmits the lesser petrosal nerve also.

3 4. The foramen spinosum (Fig. 6.32) transmits the middle meningeal artery, a meningeal branch of the mandibular nerve, and an emissary vein. 5. The canalis innominatus (Fig. 6.32) is not always present. When present it transmits the lesser petrosal nerve. 6. The emissary sphenoidal foramen (present occasionally) transmits some veins connecting the cavernous sinus to the pterygoid plexus of veins. 7. The carotid canal and the foramen lacerum: When the skull is viewed from below we see an opening on the inferior aspect of the petrous temporal bone. This is the lower opening of the carotid canal (Fig. 6.33). The canal itself passes forwards and medially through the substance of the petrous temporal bone and opens on the posterior wall of the foramen lacerum . The internal carotid artery enters the skull by passing through the carotid canal and through the upper part of the foramen lacerum. Inferiorly, the foramen lacerum is closed by a plate of cartilage. In addition to the internal carotid artery the structures passing through the carotid canal and the foramen lacerum include: (a) the sympathetic plexus on the artery; (b) and a venous plexus which connects the cavernous sinus with the pharyngeal venous plexus. In addition the foramen contains (c) the deep petrosal nerve which arises from the sympathetic plexus, in the foramen; (d) the greater petrosal nerve which enters the foramen from above; and (e) the nerve of the pterygoid canal formed by the union of (c) and (d). The only structures passing through the whole length of the foramen are (f) a meningeal branch of the ascending pharyngeal artery; and (g) some emissary veins that pierce the cartilage closing the lower end of the foramen.

Fig. 6.33. Scheme to show the structures passing through the carotid canal and the foramen lacerum.

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8. The jugular foramen consists of anterior, middle and posterior parts. The structures passing through them are as follows (Fig. 6.34). Through anterior part: Inferior petrosal sinus. Through middle part: (a) Glossopharyngeal nerve (b) Vagus nerve (c) Accessory nerve.

Fig. 6.34. Scheme to show the structures passing through the jugular foramen.

(d) Meningeal branch of ascending pharyngeal artery. Through posterior part: (a) Lower end of sigmoid sinus. (b) Emissary veins connecting the sigmoid sinus to the occipital veins. (c) Meningeal branch of the occipital artery. 9. Closely associated with the jugular foramen there are two foramina that are inconspicuous, but are important (Fig. 6.35). (a) The glossopharyngeal nerve carries secretomotor fibres for the parotid gland. These fibres leave the nerve through its tympanic branch. This branch enters a small foramen opening on the ridge separating the jugular foramen from the lower opening of the carotid canal. This opening leads into a canal called the tympanic canaliculus which passes through the substance of the petrous temporal bone to reach the middle ear. In the middle ear the fibres of the tympanic branch pass through the tympanic plexus into the lesser petrosal nerve. This nerve emerges from the petrous temporal bone on its anterior surface (i.e., into the middle cranial fossa) through the hiatus for the lesser petrosal nerve. We have already seen that the nerve then passes through the foramen ovale (or through the canalis innominatus) to reach the infratemporal fossa. (b) Another nerve traversing the substance of the petrous temporal bone is the auricular branch of the vagus. This nerve enters the bone through the mastoid canaliculus that opens on the lateral wall of the jugular fossa. It emerges from the bone through the tympanomastoid fissure (behind the external acoustic meatus).

Fig. 6.35. Scheme to show the position of the opening of the inferior tympanic canaliculus and of the mastoid canaliculus.

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10. The foramen magnum is the largest foramen in the skull. Through it the cranial cavity communicates with the vertebral canal. The structures passing through it are as follows. (a) Lower end of medulla surrounded by meninges, and accompanied by the anterior and posterior spinal arteries.

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(b) Lying in the subarachnoid space around the medulla there are (on each side) the lower end of the tonsil of the cerebellum, the vertebral artery, and the spinal root of the accessory nerve. (c) The anterior (narrow) part of the foramen magnum gives passage to the apical ligament of the dens, the superior band of the cruciform ligament, and the membrana tectoria. The alar ligaments of the dens are attached just below the lateral margin of the foramen. 11. The hypoglossal canal transmits (a) the hypoglossal nerve, (b) a meningeal branch of the ascending pharyngeal artery, and (c) an emissary vein connecting the sigmoid sinus to the internal jugular vein. 12. When present the (posterior) condylar canal transmits an emissary vein that connects the lower end of the sigmoid sinus to occipital veins. Fig. 6.36. Scheme to show the arrangement of structures passing through the foramen magnum.

13. The stylomastoid foramen gives exit to the facial nerve. It also transmits the stylomastoid branch of the posterior auricular artery.

E. Foramina to be seen on the Floor of the Cranial Fossae The foramina already seen on the base of the skull are not included in this list. 1. The apertures on the cribriform plate of the ethmoid give passage to bundles of the olfactory nerves. 2. The foramen caecum is usually blind, but sometimes it is patent and a vein passes through it and connects the veins of the nose to the superior sagittal sinus. 3. The anterior ethmoidal canals open on the suture between the orbital plate of the frontal bone and the cribriform plate, and transmit the anterior ethmoidal nerves and vessels. These

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nerves and vessels run forwards and enter the nasal cavity by passing through slit-like foramina on the sides of the crista galli. (The slits are difficult to see). 4. The posterior ethmoidal canals, which transmit the posterior ethmoidal nerves and vessels, open at the posterolateral corner of the cribriform plate. 5. The foramen rotundum opens posteriorly into the middle cranial fossa, and anteriorly into the pterygopalatine fossa. The maxillary division of the trigeminal nerve passes through the foramen: then through the upper part of the pterygopalatine fossa; and finally through the inferior orbital fissure to reach the orbit where we have already seen it. 6. The greater and lesser petrosal nerves enter the middle cranial fossa by emerging through the hiatuses for these nerves present on the anterior aspect of the petrous temporal bone. We have seen that the greater petrosal nerve descends to the foramen lacerum (Fig. 6.33) and that the lesser petrosal nerve leaves the skull through the foramen ovale, or through the canaliculus innominatus. 7. The internal acoustic meatus is seen on the posterior aspect of the petrous temporal bone. The structures entering it are: (a) the facial nerve (motor root and nervus intermedius); (b) the vestibulocochlear nerve, and (c) the labyrinthine vessels. The vestibulocochlear nerve terminates within the petrous temporal bone by supplying the membranous labyrinth. The facial nerve follows a complicated course through the bone and finally emerges on the base of the skull through the stylomastoid foramen. A little above its exit from this foramen the facial nerve gives off the chorda tympani nerve. This nerve passes through a posterior canaliculus to enter the cavity of the middle ear, which it leaves through an anterior canaliculus that opens to the outside through the medial end of the petrotympanic fissure. Here the nerve comes to lie just medial to the spine of the sphenoid. It is of interest to note that the spine is related to another nerve, the auriculotemporal, on its lateral side.

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The Nasal Cavity The nasal cavity consists of right and left halves that are separated by a nasal septum 3 (Figs. 6.37 to 6.39). The cavity opens, anteriorly, on the front of the skull through the anterior nasal aperture; and, posteriorly, on the base of the skull just above the posterior edge of the bony palate, through the right and left posterior nasal apertures. Each half of the cavity has a lateral wall, a medial wall formed by the septum, a floor formed by the upper surface of the palate, and a roof. The formation of the lateral wall is complicated and to understand it properly it has to be built up layer by layer. In figure 6.37A we see the medial surface of the maxilla, which forms the base of the lateral wall over which other bones are attached. The features to be noted are (a) the large opening of the maxillary air sinus called the maxillary hiatus; (b) the nasolacrimal groove lying behind the lower part of the frontal process; and (c) the groove for the greater palatine canal in the posteroinferior part. In figure 6.37B we see the palatine bone (perpendicular plate) overlapping the posterior part of the maxilla. By this overlapping the greater palatine groove is converted into a canal,

Fig. 6.37. Bones in the lateral wall of the nose. A. Medial aspect of maxilla. B. Palatine bone overlapping maxilla. C. Lacrimal bone and inferior nasal concha overlapping the maxilla and palatine bone. Also see figure 6.38.

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Fig. 6.38. Lateral wall of the nasal cavity seen with the ethmoid bone in place. The parts shown in dotted line can be seen only when the middle concha is lifted off.Compare with figure 6.37C.

its medial wall being formed by the palatine bone. Note also that the palatine bone overlaps the posterior part of the maxillary hiatus reducing its size. In figure 6.37C we see two additional bones. Behind the frontal process of the maxilla we see the lacrimal bone. Articulating with its lower border we see the inferior nasal concha. The lower part of the lacrimal bone, and the upper part of the inferior nasal concha (lacrimal process) convert the nasolacrimal groove of the maxilla into a canal and form its medial wall. The inferior concha is attached anteriorly to the conchal crest of the maxilla (Fig. 6.37A) and posteriorly to the conchal crest of the palatine bone (Fig. 6.37B). Its upper margin overlaps the lower part of the maxillary hiatus. Here a downward projection of the concha called the maxillary process descends deep to the rest of the concha to articulate with the lower edge of the hiatus. Another projection, the ethmoidal process juts upwards into the hiatus. The space between the concha (medially) and the maxilla and palatine bones (laterally) is the inferior meatus. In figure 6.38 we see part of the ethmoid bone overlapping the lacrimal bone and the upper parts of the maxilla and palatine bones. The relationship of the ethmoid to the nasal cavity is best visualised by the study of a coronal section through the region (Figs. 6.9, 6.42). The ethmoid bone consists of a labyrinth that is closed medially by a vertical medial plate. It is this plate that is seen in the lateral wall of the nasal cavity. The plate descends vertically from the cribriform plate; and its lower part which is free forms the middle nasal concha. Above the middle concha a smaller projection, the superior nasal concha, arises from the medial plate. The spaces deep to these conchae are called the middle and superior meatuses respectively. The middle concha almost completely hides the maxillary hiatus from view. Deep to the concha a rounded prominence

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Fig. 6.39. Main bones taking part in forming the nasal septum.

called the bulla ethmoidalis is seen in relation to the upper part of the hiatus. A little below the bulla a curved plate of bone runs downwards and backwards. This is the uncinate process of the ethmoid. Its posterior end joins the ethmoidal process of the inferior concha. The curved gap between the bulla ethmoidalis and the uncinate process is called the hiatus semilunaris. The floor of the nasal cavity is formed by the upper surface of the bony palate. We have already seen that each half of the palate is formed anteriorly by the palatine process of the maxilla, and posteriorly by the horizontal plate of the palatine bone. Several bones take part in forming the roof of the nasal cavity. From front to back these are parts of the nasal bone, the frontal bone, the cribriform plate of the ethmoid and the anterior surface of the body of the sphenoid bone. The medial wall or nasal septum (Fig. 6.39) is formed in its upper part by the perpendicular plate of the ethmoid bone (see also Fig. 6.9), and its lower part by the vomer. Anteriorly, there is a gap in the septum which is filled in by cartilage. Around the edges of the septum there are small contributions from the nasal, frontal, sphenoid, maxillary and palatine bones. The openings into the nasal cavity are described along with the paranasal sinuses (See below).

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The Paranasal Sinuses The paranasal sinuses are spaces present in bones around the nasal cavity, and into which they open (Figs. 6.40 to 6.42). We have already noted that the maxillary sinus lies within the maxilla; and that the large maxillary hiatus is considerably narrowed by projections from the palatine bone, the inferior nasal concha, the ethmoid bone and the lacrimal bone. The opening is further narrowed by the mucous membrane covering these bones and the sinus usually opens into middle meatus of the nasal cavity by an opening in the lower part of the hiatus semilunaris (Fig. 6.41). The right and left frontal sinuses are present in the part of the frontal bone deep to the superciliary arches. Each sinus lies deep to a triangular area the angles of which are placed as follows: (a) at the nasion, (b) at a point about 3 cm above the nasion, and (c) at a point on the supraorbital margin at the junction of the medial one third with the lateral two thirds. The sinus extends for some distance into the orbital plate of the frontal bone between the roof of the orbit and the floor of the anterior cranial fossa. Each frontal sinus usually opens into the middle meatus through a funnel like space, the ethmoidal infundibulum (Fig. 6.41) which is continuous with the upper end of the hiatus semilunaris. The right and left sphenoidal sinuses are present in the body of the sphenoid bone. Each sinus opens into the corresponding half of the nasal cavity through an aperture on the anterior aspect of the body of the sphenoid. The part of the nasal cavity into which the sinus opens lies above the superior nasal concha and is called sphenoethmoidal recess (Fig. 6.41).

Fig. 6.40. Lateral wall of the nasal cavity seen after removal of the medial plate of the ethmoid bone to expose the ethmoidal air sinuses.

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The ethmoidal air sinuses are located within the lateral part (or labyrinth) of the ethmoid bone. Each labyrinth (right or left) is bounded medially by the medial plate and laterally by the orbital plate. The ethmoidal air sinuses lie between these plates. They can be divided into anterior, middle and posterior groups. In figure 6.40 they are seen from the medial side after removing the superior and middle nasal conchae, and the medial plate. The walls of some of these sinuses 3 are incomplete. In the intact skull they are completed by parts of the frontal, maxillary, lacrimal, sphenoidal and palatine bones. The anterior ethmoidal sinuses open into the ethmoidal infundibulum, or into the upper part of the hiatus semilunaris. The middle ethmoidal sinuses open on or near the bulla ethmoidalis. The posterior ethmoidal sinuses open into the superior meatus.

Other Apertures in the Nasal Cavity In addition to the anterior and posterior nasal apertures, and the openings of the paranasal sinuses, we see the following openings in the nasal cavity. (a) The nasolacrimal canal opens into the inferior meatus.

Fig. 6.41. Schematic diagram to show the positions of the openings of paranasal sinuses into the nasal cavity.

(b) The sphenopalatine foramen opens behind the superior meatus, just above the posterior end of the middle concha (Fig. 6.38). This foramen has been seen in the medial wall of the pterygopalatine fossa. (c) The nasal cavity communicates with the anterior cranial fossa through numerous apertures in the cribriform plate of the ethmoid bone (Fig. 6.28), and through the anterior ethmoidal canals. (d) In the anterior part of the floor of the nasal cavity there is a funnel shaped opening that leads into the incisive

Fig. 6.42. Scheme to show the parts of the ethmoid bone.

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canals which open on the lower surface of the palate. Ossification of the Skull The development and ossification of the skull is complex, and details of the process are beyond the scope of medical students. The following account is a summary of the most relevant features. The skull develops from mesenchyme surrounding the developing brain. The mesoderm of the occipital myotomes, the otic capsule, the nasal capsule and the first branchial arch also contributes to the formation of the skull. The mesenchyme shows condensations in regions where the skull bones are to develop. A number of chondrification centres appear in relation to the base of the skull. The cartilages formed do not correspond to individual bones, but follow a complicated pattern. The base of the skull is formed by ossification in relation to these cartilages. The mesenchyme that is to form the sides and vault of the skull, and also the facial skeleton is not chondrified, but is converted into bone by intramembranous ossification. It follows that some bones of the skull are formed in membrane, some in cartilage, and some partly in membrane and partly in cartilage, as listed below. (a) Bones that are formed entirely in membrane:

These are the frontal, parietal, zygomatic, palatine, nasal, and lacrimal bones, the maxilla and the vomer. (b) Bones that are formed entirely in cartilage:

These are the ethmoid and the inferior nasal concha. (c) Bones that are formed partly in cartilage and partly in membrane:

These are the occipital, sphenoid and temporal bones; and the mandible. The times at which individual skull bones begin to ossify is highly variable. Centres of ossification appear in many of them in the 7th or 8th prenatal week; but in some ossification begins after birth. The number of ossification centres is also highly variable. The zygomatic, palatine, lacrimal and nasal bones; the vomer; and the inferior nasal concha have only one centre each. The parietal bone ossifies from two centres that appear in the region of the future tuber. Also see fontanelles below. The frontal bone has two centres on each side. At birth the bone is in two halves. The two halves occasionally remain separate and are united by a midline suture called the metopic suture.

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The ethmoid bone has three centres of ossification: one for the perpendicular plate, and one for each labyrinth. Each maxilla has one main centre, but additional centres appear in its anterior part. There is considerable controversy on whether or not the anterior centres correspond to the premaxilla.

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The occipital bone ossifies from several centres. In the newborn this bone consists of separate squamous, condylar (lateral) and basilar parts that are united by cartilage. These parts fuse with one another by the 6th year. The basilar part of the occipital bone fuses with the corresponding part of the sphenoid bone between 18 and 25 years. The sphenoid bone also ossifies from several centres. At birth the bone is in three pieces: one central, and right and left lateral. The central piece consists of the body and lesser wings; while each lateral piece consists of a greater wing and a pterygoid process. The pieces unite during the first year of life. The body of the sphenoid fuses with the basilar part of the occipital bone between 18 and 25 years of age. The temporal bone ossifies from several centres. The squamous, tympanic, and styloid parts ossify independently. The petrous and mastoid parts constitute one petromastoid morphological element, that has several centres of ossification. The squamous part is the first to ossify. At birth the tympanic part is rudimentary and is U-shaped (It is miscalled the tympanic ring). Subsequently, this part grows laterally forming the bony part of the external acoustic meatus. It also extends backwards to surround the base of the styloid process, and medially to reach the carotid canal. At birth the mastoid part is poorly developed and a mastoid process is not seen. Postnatally, mastoid air cells develop leading to formation of the mastoid process (by about 2 years of age). The facial canal and the stylomastoid foramen are at first near the lateral surface of the bone, but with the formation of the mastoid process they become deeper.

The Fontanelles In the skull of the new born, there are some gaps in the vault of the skull that are filled by membrane. These gaps are called fontanelles or fonticuli. They are located in relation to the angles of the parietal bone as follows. (a) The anterior fontanelle is large and rhomboid in shape. It lies at the junction of the sagittal, coronal and frontal sutures. (Note that at birth the frontal bone is in two halves that are separated by a frontal suture). (b) The posterior fontanelle is triangular. It lies at the junction of the sagittal and lambdoid sutures. (c) The sphenoidal (anterolateral) fontanelle is present in relation to the antero-inferior angle of the parietal bone, where it meets the greater wing of the sphenoid. (d) The mastoid fontanelle (posterolateral) is present in relation to the posteroinferior angle of the parietal bone (which meets the mastoid bone).

The fontanelles disappear (by growth of the bones around them) at different ages after birth. The posterior and sphenoidal fontanelles disappear within two or three months after birth; the mastoid fontanelle by the end of the first year; and the anterior fontanelle by the middle of the second year.

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7 Individual Bones of the Skull

The Mandible The mandible is the bone of the lower jaw and bears the lower teeth (Figs. 7.1 to 7.5). It consists of an anterior U-shaped body, and of two rami (right and left) that project upwards from the posterior part of the body. The bone has internal (or medial) and external (or lateral) surfaces. The body has an upper part that bears the teeth (alveolar process), and a lower border that is called the base. The ramus has a posterior border, a sharp anterior border, and a lower border that is continuous with the base of the body. The posterior and inferior borders of the ramus meet at the angle of the mandible. The anterior border of the ramus is continued downwards and forwards on the lateral surface of the body as the oblique line. This line ends anteriorly near the mental tubercle (see below). A little above the anterior part of the oblique line we see the mental foramen which lies vertically below the second premolar tooth. Just below the incisor teeth the external surface of the ramus shows a shallow incisive fossa. Arising from the upper part of the ramus there are two processes. The anterior of these is the coronoid process. It is flat (from side to side) and triangular. The posterior or condylar process is separated from the coronoid process by the mandibular notch. The upper end of the condylar process is expanded to form the head of the mandible. Fig.7.1. Mandible seen from above.

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The head is elongated transversely and is convex both transversely and in an anteroposterior direction. It bears a smooth articular surface that articulates with the mandibular fossa of the temporal bone to form the temporomandibular joint. The part immediately below the head is constricted and forms the neck. Its anterior surface has a rough depression called the pterygoid fovea.

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In figure 7.3 the mandible is seen from the medial side. A little above the centre of the medial surface of the ramus we see the mandibular foramen. It leads into the mandibular canal which runs forwards in the substance of the mandible. The medial margin of the foramen is formed by a projection called the lingula. Beginning just behind the lingula and running downwards and forwards we see the mylohyoid groove. A little above and anterior to the mylohyoid groove, the inner surface of the body of the mandible is marked by a ridge called the mylohyoid line. The posterior end of this line lies a little below and behind the third molar tooth. From here the line runs downwards and forwards to reach the symphysis menti (see below). The mylohyoid line divides the inner surface of the body into a sublingual fossa (lying above the line), and a submandibular fossa (lying below the line).

Fig. 7.2. Right half of mandible seen from the lateral side.

Just below the anterior end of the mylohyoid line the base of the mandible is marked by a deep digastric fossa. In the newborn the mandible consists of right and left halves that are joined to each other at the symphysis menti; but in later life the halves fuse to form one bone. When viewed from the front (Fig. 7.4) the region of the symphysis menti is usually marked by a slight ridge. Inferiorly, the ridge expands to form a

Fig. 7.3. Right half of the mandible seen from the medial side.

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triangular raised area called the mental protuberance. The lateral angles of the protuberance are prominent and constitute the mental tubercles. The posterior aspect of the symphysis menti also shows a median ridge (Fig. 7.5) the lower part of which is enlarged and may be divided into upper and lower parts called the mental spines or genial tubercles.

Attachments and Relations

Fig. 7.4. Median part of the mandible, anterior aspect.

A. The muscles attached on the external aspect of the mandible are as follows (Fig. 7.6) 1. The masseter is inserted into the lateral surface of the ramus and of the angle. 2. The buccinator arises from the outer surface of the body just below the molar teeth. 3. The depressor labii inferioris arises from the anterior part of the oblique line.

Fig. 7.5. Median part of mandible, posterior aspect.

4. The depressor anguli oris arises from the oblique line behind and below the origin of the depressor labii inferioris. 5. The mentalis arises from the incisive fossa (just below the incisor teeth). 6. Some fibres of the platysma are inserted into the lower border of the body.

Fig. 7.6. Attachments on the mandible as seen from the lateral side.

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B. The muscles attached on the internal surface of the mandible are as follows (Figs. 7.7, 7.8) 1. The temporalis is inserted into the medial surface of the coronoid process including its apex, and its anterior and posterior borders. The insertion extends downwards along the anterior 3 border of the ramus (Also see Fig. 7.6). 2. The lateral pterygoid is inserted into the fovea on the anterior aspect of the neck. 3. The medial pterygoid is inserted into the medial surface of the angle and the adjoining part of the ramus.

4. The anterior belly of the digastric arises from the digastric fossa (on the anterior part of the base near the midline).

5. The genioglossus takes origin from the upper mental spine.

6. The geniohyoid takes origin from the lower mental spine.

Fig. 7.7. Attachments on the mandible as seen from the medial side.

7. The mylohyoid arises from the mylohyoid line. 8. Some fibres of the superior constrictor of the pharynx take origin from the posterior end of the mylohyoid line (near the attachment of the pterygomandibular raphe). Fig. 7.8. Region of the symphysis menti, showing attachments, seen from behind.

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C. The ligaments attached to the mandible are as follows 1. The capsule of the temporomandibular joint is attached along the margins of the articular surface. 2. The lateral temporomandibular ligament is attached to the lateral aspect of the neck of the mandible. 3. The sphenomandibular ligament is attached to the lingula of the mandible. 4. The stylomandibular ligament is attached to the angle and posterior border of the ramus of the mandible. 5. The pterygomandibular raphe is attached to the posterior end of the mylohyoid line.

D. Relations to nerves and vessels 1. The masseteric nerve and vessels pass through the mandibular notch. 2. The inferior alveolar nerve and vessels enter the mandibular canal (which lies within the bone) through the mandibular foramen. 3. The mylohyoid nerve and vessels run forwards in the mylohyoid groove. 4. The mental nerve and vessels emerge through the mental foramen. 5. The facial artery is closely related to the mandible. Its initial part lies deep to the ramus, near the angle. The artery then runs downwards and forwards deep to the ramus being separated from the bone by the medial pterygoid muscle. It reaches the lower border of the body of the mandible at the anteroinferior angle of the masseter. The artery then runs upwards and forwards superficial to the body of the mandible.

E. Other relations. 1. Part of the bone adjoining the alveolar border is covered by mucosa. 2. The lingual nerve is closely related to the medial aspect of the body just above the posterior end of the mylohyoid line. 3. The sublingual gland lies over the sublingual fossa; and the submandibular gland over the submandibular fossa. The parotid gland is related to the upper part of the posterior border of the ramus.

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Development and Ossification of the Mandible The greater part of the mandible is ossified in membrane in the mesenchyme of the mandibular process. The ventral part of Meckel’s cartilage becomes embedded in the bone. Ossification of the coronoid and condyloid processes is preceded by formation of secondary cartilage in these 3 situations. The mandible is one of the first bones in the body to start ossifying (being next in this respect only to the clavicle). Each half of the bone is formed from one centre of ossification that appears (near the mental foramen) during the 6th week of fetal life. Small secondary centres may appear for the genial tubercles. At birth the bone is in two halves that are united at a fibrous joint called the symphysis menti. The two halves unite between the first and third years of age. Age Changes in the Mandible Apart from fusion of the two halves of the bone, and the progressive increase in size, the following points are noteworthy: 1. The prominence of the chin is absent at birth. It forms during the first and second year. 2. At birth the mental foramen lies close to the inferior margin of the body of the mandible. It gradually shifts upwards and in the adult it lies midway between the upper and lower borders of the body. With loss of teeth and alveolar bone in old age the foramen shifts nearer to the upper border. The direction of the foramen also changes with age. In the young it opens forwards, but in the adult it opens backwards.

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The Maxilla The right and left maxillae are seen when the skull is viewed from the front (Figs. 6.4, 6.8). They bear the upper teeth. Each maxilla takes part in forming the palate, the floor and lateral wall of the nasal cavity, and the floor of the orbit. Each maxilla has a body, an alveolar process, a zygomatic process, a frontal process, and a palatine process (Figs. 7.9, 7.10).

The Body The body has anterior (actually anterolateral), posterior, medial and superior surfaces. Inferiorly, the body is continuous with the alveolar process which has sockets for the teeth. The body encloses the maxillary air sinus. The upper margin of the anterior surface (of the maxilla) becomes continuous with the superior surface at the inferior margin of the orbit. Medially, the anterior surface ends at the nasal notch which bounds the anterior nasal aperture. Other features to be seen on the anterior surface have been described earlier (Fig. 6.8). These are the infraorbital foramen, the incisive and canine fossae, the canine eminence, and the anterior nasal spine.

Fig. 7.9. Right maxilla, lateral aspect.

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Fig. 7.10. Right maxilla, medial aspect.

The superior (or orbital) surface forms the floor of the orbit (Fig. 6.11). Posterolaterally it forms the lower margin of the inferior orbital fissure. The infraorbital groove runs forwards over the orbital surface. This groove starts at the inferior orbital fissure and ends a short distance from the inferior orbital margin by becoming continuous with the infraorbital canal (which opens on the anterior surface at the infraorbital foramen). Anteromedially, the orbital surface has a notch which forms the lateral margin of the upper opening of the nasolacrimal canal. The margins of the orbital surface articulate with the zygomatic, ethmoid, and lacrimal bones, and with the orbital process of the palatine bone. The medial (or nasal) surface of the maxilla takes part in forming the lateral wall of the nose. The features on this surface have already been examined (Figs. 6.37, 7.10). They include the maxillary hiatus, the nasolacrimal groove, the groove for the greater palatine canal, and the conchal crest. This aspect of the bone comes into intimate contact with the palatine, ethmoid and lacrimal bones, and with the inferior nasal concha. The posterior (or infratemporal) surface forms the anterior wall of the infratemporal fossa and of the pterygopalatine fossa (Figs. 6.18, 6.19). Inferiorly, this surface bears a projection, the maxillary tuberosity which is the posterior end of the alveolar process. The upper margin of this surface becomes continuous with the orbital surface at the inferior orbital fissure. Here the surface is grooved by the maxillary nerve as the latter runs forwards to reach the infraorbital groove. Lower down the infratemporal surface bears small openings for the posterior superior alveolar nerves and vessels. The infratemporal surface meets the pterygoid process of the sphenoid bone at the lower end of the pterygomaxillary fissure.

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The Zygomatic Process The zygomatic process of the maxilla is thick and strong. It projects laterally from the junction of the anterior and infratemporal surfaces and ends by articulating with the zygomatic bone.

The Palatine Process The palatine process passes medially and forms the greater part of the palate. The inferior aspect of the palatine process has been examined earlier. The features seen include the intermaxillary suture, the incisive fossa and incisive foramina, and a vascular groove for the greater palatine vessels. Posteriorly, the palatine process meets the horizontal plate of the palatine bone at the palatomaxillary suture. The upper surface of the palatine process forms the floor of the nasal cavity. On this surface, bone is thickened along the intermaxillary suture to form a nasal crest which articulates with the vomer, and contributes to the formation of the nasal septum. The crest is more pronounced at its anterior end where it is seen in the floor of the anterior nasal aperture as the anterior nasal spine (Fig. 6.8).

Frontal Process The frontal process of the maxilla extends upwards and medially from the body. Its upper edge meets the nasal part of the frontal bone. Medially (and anteriorly) it articulates with the nasal bone; and posteriorly it articulates with the lacrimal bone (Fig. 6.8). The frontal process has external and internal surfaces. The external surface bears a vertical ridge called the anterior lacrimal crest: this crest is continuous with the inferior orbital margin. Behind this crest there is a vertical groove which forms the lacrimal groove along with the groove on the lacrimal bone.

Determination of Side The maxilla can be correctly orientated and its side determined by examining the alveolar process alone. The alveolar process bearing the teeth (or sockets for them) lies inferiorly, and laterally. The sockets for the teeth reach the midline anteriorly.

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The Zygomatic Bone 3 the The zygomatic bone is seen when the skull is viewed from the front (Figs. 6.4, 6.8) or from side (Figs. 6.9, 6.14). It forms the prominence of the cheek. Parts of it are seen in the orbit (Fig. 6.11), and in the anterior wall of the temporal and infratemporal fossae (Fig. 6.18). The zygomatic bone consists of a body, a frontal process, and a temporal process. The body articulates anteromedially, with the maxilla. The frontal process articulates with the zygomatic process of the frontal bone. The temporal process articulates with the zygomatic process of the temporal bone to form the zygomatic arch. The body of the zygomatic bone has lateral, temporal, and orbital surfaces. The lateral surface forms the prominence of the cheek. It is perforated by the zygomaticofacial foramen (or foramina). The temporal surface is directed medially and posteriorly. It forms the anterior wall of the temporal fossa (and makes a small contribution to the anterior wall of the infratemporal fossa). It is pierced by the zygomaticotemporal foramen. The orbital surface forms part of the lateral wall of the orbit (Fig. 6.11). Posteriorly, this surface meets the greater wing of the sphenoid from which it is partially separated by the inferior orbital fissure. Medially it meets the orbital surface of the maxilla.

Fig. 7.11. Right zygomatic bone, lateral aspect.

The lateral surface of the zygomatic bone is demarcated by four borders: anterosuperior (or orbital), anteroinferior (or maxillary), posterosuperior (or temporal) and posteroinferior. The anterosuperior border is curved: it forms parts of the inferior and lateral orbital margins and separates the lateral surface from the orbital surface. The anteroinferior border articulates with the zygomatic process of the maxilla. The posterosuperior border extends from the frontozygomatic suture to the zygomatico-temporal suture: Fig. 7.12. Right zygomatic bone, medial aspect.

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it separates the lateral and temporal surfaces. The posteroinferior border forms the anterior part of the lower border of the zygomatic arch. It extends from the zygomatico-maxillary suture to the zygomatico-temporal suture. The temporal surface ends medially in a posteromedial border which articulates with the greater wing of the sphenoid (in the anterior wall of the temporal fossa: Fig. 6.18) and inferiorly with the maxilla. Note that the entire area between the anteroinferior and posteromedial borders is rough for articulation with the maxilla. Determination of side The bone can be correctly orientated and its side determined by looking at the orbital margin. The orbital margin lies at the upper end of the anterior aspect. This margin contributes to the inferior and lateral margins of the orbit.

The Frontal Bone The main part of the frontal bone forms the wall of the cranial cavity in the region of the forehead. It ends inferiorly in a median downward projection which constitutes the nasal part of the bone. On either side of the nasal part the lower edge of the bone forms the superior margin of the corresponding orbit. Passing backwards from each orbital margin there is an orbital plate that forms the greater part of the roof of the orbit. The right and left orbital plates constitute the orbital part of the frontal bone. Lateral to the orbital margin there is a projection called the zygomatic process.

The Main Part The main part of the frontal bone has external and internal surfaces. The greater part of the external surface corresponds to the forehead. This part is bounded on each side by a prominent ridge that is continuous anteriorly with the upper border of the zygomatic process, and posteriorly with the temporal lines. The part of the external surface behind this ridge, and below the temporal lines forms part of the floor of the temporal fossa. The features to be seen on the part of the external surface corresponding to the forehead have been described earlier (Figs. 6.4, 6.8). These are the frontal tuber (or eminence), the superciliary arches, the glabella, the supraorbital notch (or foramen) and the frontal notch or foramen. The internal surface (Fig. 6.12) is marked, by a median sulcus for the superior sagittal sinus. Traced downwards the lips of this sulcus fuse to form a median ridge called the frontal crest. At the lower end of the crest there is the foramen caecum.

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Fig. 7.13. Frontal bone seen from the front.

Fig. 7.14. Fontal bone, seen from below.

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Zygomatic Process The zygomatic process passes downwards and laterally to meet the frontal process of the zygomatic bone.

Orbital part The orbital plates (right and left) of the frontal bone are separated by a wide notch which is filled, in the intact skull, by the ethmoid bone (Fig. 7.14). Immediately anterior to the notch there are the openings into the right and left frontal air sinuses. Immediately lateral to the notch, the inferior aspect of the orbital plate shows two or three depressions: these are the upper parts of ethmoidal air cells that are completed in the intact skull by similar depressions on the labyrinth of the ethmoid bone. More laterally, the inferior surface of each orbital plate forms the greater portion of the roof of the corresponding orbit. The anterolateral part of the roof shows a shallow depression, the lacrimal fossa, for the lacrimal gland. The anteromedial part of the roof bears a small depression, the trochlear fossa. The superior surface of the orbital plate of the frontal bone forms the greater part of the floor of the anterior cranial fossa. (Also see Figs. 6.9, 6.11).

Nasal Part The nasal part of the frontal bone projects downwards between the right and left supraorbital margins. The lower part of the projection lies behind the nasal bones and the frontal process of the maxillae, and helps to support the bridge of the nose. The nasal part bears a median projection, the nasal spine, which contributes to the nasal septum (Fig. 6.38).

Articulations The frontal bone articulates posteriorly with the right and left parietal bones (at the coronal suture); and with the greater wing of the sphenoid. Through its zygomatic process it articulates with the zygomatic bone. The nasal part articulates with the nasal bones, and with the frontal processes of the maxillae. The nasal spine meets the perpendicular plate of the ethmoid bone. The orbital parts articulate with the greater and lesser wings of the sphenoid, with the orbital plate of the ethmoid bone, and with the lacrimal bone of the corresponding side.

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The Parietal Bone 3 The right and left parietal bones form the greater part of the roof and side walls of the cranial cavity (Figs. 6.12 to 6.14). Each bone has an external surface and an internal surface. The features to be seen on the external surface are the parietal tuber (or eminence), the superior and inferior temporal lines, and the parietal foramen. These have been described earlier (Figs. 6.12, 6.14, 7.15). The internal surface (Fig. 7.16) bears grooves for the frontal and parietal branches of the middle meningeal vessels. The posteroinferior angle bears a groove for part of the sigmoid sinus. There is a groove for the superior sagittal sinus along the upper (sagittal) border.

Articulations The right and left parietal bones articulate with each other at the sagittal suture.Anteriorly, each parietal bone articulates with the frontal bone at the coronal suture.

Fig. 7.15. Right parietal bone, lateral aspect.

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The anteroinferior angle articulates with the greater wing of the sphenoid. The inferior border articulates with the temporal bone (squamous and mastoid), and the posterior border with the occipital bone (at the lambdoid suture).

Determination of side The side to which a given parietal bone belongs can be determined using the following facts. 1. The superior or sagittal border is straight, while the inferior border has an irregular shape. 2. The posterior aspect can be distinguished because the posteroinferior angle bears a groove (for the sigmoid sinus). 3. The medial surface is concave, while the lateral surface is convex.

Fig. 7.16. Right parietal bone, medial aspect.

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The Occipital Bone 3 to The occipital bone is unpaired. It lies in the posterior part of the skull (Figs. 6.5 to 6.7, 6.12 6.15, 6.26, 6.30, 7.17, 7.18). The bone is pierced by the foramen magnum. The part behind the foramen magnum is the squamous part; the part anterior to the foramen magnum is the basilar part; and the parts on either side of the foramen are the lateral or condylar parts.

Squamous Part The squamous part contributes to the posterior wall of the vault of the skull. It has external and internal surfaces. The features to be seen on the external surface have been examined

Fig. 7. 17. Occipital bone, anterosuperior view.

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(Figs. 6.13, 7.17). These are the external occipital protuberance; the external occipital crest, and the highest, superior and inferior nuchal lines. The internal surface of the squamous part is marked by four deep fossae (Fig. 7.18). The area where the fossae meet is raised to form the internal occipital protuberance. Above the protuberance there a wide median groove for the superior sagittal sinus; and on either side of the protuberance there is an equally wide groove for the transverse sinus. These grooves have prominent lips. Inferior to the protuberance the internal surface bears a median ridge called the internal occipital crest.

The Basilar Part The basilar part of the occipital bone lies in front of the foramen magnum. In the adult it is directly continuous with the body of the sphenoid, but in the young the two are separated by a plate of cartilage. The inferior surface of the basilar part bears a small prominence called the pharyngeal tubercle (Fig. 6.26). The superior surface of the basilar part forms the sloping median portion of the anterior wall of the posterior cranial fossa (clivus) (Fig. 6.30).

Fig. 7.18. Occipital bone, posteroinferior view.

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The Lateral Part The lateral parts of the occipital bone have superior and inferior surfaces. The features to be seen on the inferior surface have been examined (Fig. 6.26). They include the occipital condyles, the hypoglossal canal, the condylar fossa, the condylar canal, the jugular process, the 3 jugular fossa and the jugular foramen. The superior surface of the lateral part of the occipital bone forms part of the floor of the posterior cranial fossa (Fig. 6.30). It bears an elevation, the jugular tubercle. The superior aspect of the jugular process bears a deep groove for the lower part of the sigmoid sinus. The groove is continuous with the jugular foramen.

Articulations The squamous part articulates (on each side) with the corresponding parietal bone at the lambdoid suture; and with the corresponding mastoid temporal bone at the occipitomastoid suture. The anterior margin of the lateral part of the bone meets the petrous temporal, the two being partially separated by the jugular fossa. Anteriorly, the basilar part is separated from the apex of the petrous temporal bone by the foramen lacerum.

Fig. 7.19. Right temporal bone, lateral aspect.

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The Temporal Bone Each temporal bone (right or left) is made up of squamous, petrous, mastoid, tympanic and styloid parts (Figs. 6.5 to 6.7, 6.13 to 6.17, 6.25, 6.26, 630, 7.19 to7.21). Its lateral aspect is marked by a prominent zygomatic process and by the external acoustic meatus.

The Squamous Part The squamous part contributes to the lateral wall of the skull. It also forms part of the base of the skull, and part of the floor of the middle cranial fossa. It has external (or temporal) and internal (or cerebral) surfaces. Arising from its external aspect there is the zygomatic process that joins the temporal process of the zygomatic bone to form the zygomatic arch (or zygoma). Inferiorly, the squamous part bears the mandibular fossa for articulation with the head of the mandible. Some features to be seen on the lateral aspect of the squamous temporal bone have been described (Figs. 6.14 to 6.17). These include the temporal lines, the supramastoid crest, the anterior and posterior roots of the zygomatic process, the tubercle of the root of the zygoma, the postglenoid tubercle and the suprameatal triangle. When we examine the inferior aspect

Fig. 7.20. Right temporal bone, crnial aspect.

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of the squamous temporal bone we see the infratemporal surface, the mandibular fossa and the articular tubercle (Figs. 6.25, 6.26). The cerebral surface of the squamous part forms the lateral portion of the floor, and the lateral wall, of the middle cranial fossa. This surface shows vascular grooves (Fig. 6.30).

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The Mastoid Part The mastoid part of the temporal bone lies behind the external acoustic meatus. It shows a large downward projection called the mastoid process (Figs. 6.15, 6.16, 6.26). Medial to the mastoid process there is a deep mastoid notch. Near the anterior end of the notch we see the stylomastoid foramen. Medial to the mastoid notch there is a groove for the occipital artery. Posteriorly, the mastoid part of the temporal bone meets the occipital bone at the occipitomastoid suture. A mastoid foramen is present on or near this suture. The internal surface of the mastoid temporal is seen in the lateral part of the floor of the posterior cranial fossa (Fig. 6.30). It is marked by the groove for the sigmoid sinus, and by the internal opening of the mastoid foramen. Fig. 7.21. Right temporal bone, seen from below.

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Within its substance the mastoid temporal bone contains several air filled spaces called the mastoid air cells. The largest of these is the mastoid antrum, which is closely related to the middle ear.

The Petrous Part The petrous part of the temporal bone lies in the base of the skull in between the sphenoid bone, anteriorly, and the occipital bone, posteriorly. It is seen when the skull is viewed from below, and also in the floor of the middle and posterior cranial fossae. It has anterior, posterior, and inferior surfaces, and an apex which points forwards and medially. The apex lies in the angle between the basilar part of the occipital bone (posteromedially) and the greater wing of the sphenoid (anterolaterally). It forms the posterior margin of the foramen lacerum. This foramen separates the apex from the body of the sphenoid bone, and from the basilar part of the occipital bone. The anterior surface forms the sloping posterior part of the floor of the middle cranial fossa. The features to be seen on this surface have been examined (Fig. 6.30). They include the trigeminal impression, the hiatus for the greater petrosal nerve, the hiatus for the lesser petrosal nerve, the arcuate eminence and the tegmen tympani. The posterior surface of the petrous temporal forms the lateral part of the sloping anterior wall of the posterior cranial fossa. This surface presents the opening of the internal acoustic meatus. Posterolateral to this opening a slit in the bone leads into a canal called the aqueduct of the vestibule. The anterior and posterior surfaces are separated by a sharp superior border. This border separates the middle and posterior cranial fossae. The border is grooved by the superior petrosal sinus. The inferior surface of the petrous temporal bone presents the lower opening of the carotid canal. The canal passes medially through the substance of the petrous temporal bone to open into the posterior wall of the foramen lacerum. Behind the opening of the carotid canal the petrous temporal forms the anterior wall of the jugular fossa, and of the jugular foramen. On the ridge between the opening of the carotid canal and the jugular fossa we see a small opening that leads into the canaliculus for the tympanic nerve. On the lateral wall of the jugular fossa there is the opening of the mastoid canaliculus. The middle ear, and the internal ear, lie within the substance of the petrous part of the temporal bone. Associated with the middle ear there is the bony auditory tube, and the canal for the tensor tympani.

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The Tympanic Part The tympanic part of the temporal bone is in the form of a plate of bone called the tympanic plate (Fig. 6.16). This plate lies between the mandibular fossa and the external acoustic meatus. It forms the anterior wall, the inferior wall, and the lower part of the posterior wall of the 3 external acoustic meatus. The plate has a rough lateral margin which gives attachment to the cartilaginous part of the meatus. Posteriorly, the tympanic plate forms a sheath for the base of the styloid process.

The Styloid Process The styloid process is attached to the inferior aspect of the temporal bone. It is thin and pointed, and variable in length (usually about 2.5cm) (Figs. 6.16, 6.30). It is directed downwards and forwards. Its base is ensheathed by the tympanic plate. The stylomastoid foramen lies just behind the base of the styloid process. Articulations of the Temporal Bone The articular tubercle and the mandibular fossa articulate with the head of the mandible to form the temporo-mandibular joint. The zygomatic process articulates with the temporal process of the zygomatic bone. Anteriorly, the squamous and petrous parts of the bone articulate with the greater wing of the sphenoid. Posteriorly, the petrous and mastoid parts articulate with the occipital bone. Superiorly, the squamous part articulates with the corresponding parietal bone. Determination of Side The side to which a given temporal bone belongs can be found by remembering that: 1. The zygomatic process is on the lateral side of the bone and points forwards. 2. The mastoid and styloid processes point downwards.

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The Sphenoid Bone The sphenoid bone is unpaired. It forms the middle part of the base of the skull. Parts of it extend into the lateral wall of the vault, and into the orbit (Figs. 6.6, 6.7, 6.14 to 6.18, 6.21 to 6.23, 6.28 to 6.30 ,7.22, 7.23). The sphenoid consists of a median part, the body, right and left greater wings, right and left lesser wings, and right and left pterygoid processes.

The Body The body of the sphenoid bone has superior, inferior, anterior, posterior, and right and left lateral surfaces. The inferior surface of the body lies in the roof of the posterior part of the nasal cavity and in the roof of the nasopharynx. Projecting downwards from the body there is a median ridge called the rostrum (which fits into the gap between the alae of the vomer (Fig. 6.22). The superior surface of the body forms the median part of the floor of the (posterior part of the) anterior cranial fossa, and of the median part of the middle cranial fossa. The features to be seen here have been examined (Figs. 6.28, 6.29). They include the jugum sphenoidale, the

Fig. 7.22. Sphenoid bone, anterior aspect.

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Fig. 7.23. Sphenoid bone, posterior aspect.

sulcus chiasmaticus, the tuberculum sellae, the hypophyseal fossa, and the dorsum sellae with the posterior clinoid processes. The lateral surfaces of the body of the sphenoid are also seen in the floor of the middle cranial fossa. Each lateral surface is marked by the carotid groove. Posteroinferiorly, the body of the sphenoid is continuous with the basilar part of the occipital bone. Along with the latter it forms the median part of the sloping anterior wall (clivus) of the posterior cranial fossa. The anterior surface of the body of the sphenoid takes part in forming the roof of the nasal cavity. This surface can be seen only in the disarticulated bone (Fig. 7.22). It bears a median sphenoidal crest on either side of which there is the opening of the corresponding sphenoidal air sinus. The lower margin of each opening is formed by a thin plate of bone called the sphenoidal concha. The sphenoidal air sinuses lie within the body of the sphenoid.

The Greater Wings The greater wings of the sphenoid extend laterally and upwards from each side of the body. Each greater wing has cerebral, lateral and orbital surfaces.

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The cerebral surface is concave. It forms part of the floor of the middle cranial fossa (Figs. 6.28, 6.29). Anteriorly and medially this surface has a sharp edge which is separated from the lesser wing by the superior orbital fissure. Just below the medial end of the fissure we see the foramen rotundum. Posteromedially, the greater wing is separated from the apex of the petrous temporal bone by the foramen lacerum. Near the posterior margin of the cerebral surface of the greater wing we see three or four foramina. These are the foramen ovale, the foramen spinosum, the emissary sphenoidal foramen, and sometimes the canaliculus innominatus. The lateral surface of the greater wing is convex. It is divisible into an upper part, the temporal surface; and a lower part, the infratemporal surface by the infratemporal crest. The features to be seen on the infratemporal surface have been described (Figs. 6.18, 6.25). They include the foramen ovale, the foramen spinosum, the emissary sphenoid foramen, the canaliculus innominatus, the spine of the sphenoid, and the groove for the auditory tube. When viewed from the front the greater wing presents an orbital surface. We have seen that this surface forms the posterior part of the lateral wall of the orbit (Fig. 6.11). Medially, it has a free edge that forms the infero-lateral margin of the superior orbital fissure. Inferiorly, it forms the upper boundary of the inferior orbital fissure.

The Lesser Wings The lesser wings of the sphenoid pass laterally from the anterior and upper part of the body. Each wing is attached to the body of the sphenoid by two roots (anterior and posterior). The optic canal lies between these roots and the body of the sphenoid. The medial part of the lesser wing bears a backward projection called the anterior clinoid process. The lesser wing has superior and inferior surfaces. The superior surface forms part of the floor of the anterior cranial fossa (including its sharp posterior edge) (Fig. 6.28). The inferior surface forms the posterior part of the roof of the orbit (Fig. 6.11). It forms the upper boundary of the superior orbital fissure.

The Pterygoid Processes Each pterygoid process projects downwards from the junction of the body and greater wing of the sphenoid (Figs. 6.16 to 6.18, 6.23, 6.24). The process consists of medial and lateral pterygoid plates. In Fig. 7.22 note that the upper part of the pterygoid process has an anterior surface which forms the posterior wall of the pterygopalatine fossa. On this surface we see the anterior opening of the pterygoid canal. (The posterior opening of the pterygoid canal is located just above the scaphoid fossa, in the anterior wall of the foramen lacerum). A little above and lateral to this opening we see the anterior opening of the foramen rotundum.

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Articulations of the Sphenoid Bone The body of the sphenoid is continuous posteroinferiorly with the basilar part of the occipital bone. Anteriorly, it articulates with the ethmoid bone. The sphenoidal crest articulates with the perpendicular plate of the ethmoid and forms a small part of the nasal septum.

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Each greater wing articulates, posteriorly, with the petrous temporal; posterolaterally, with the squamous temporal; anteromedially with the frontal bone; anteriorly and laterally with the zygomatic bone; and superiorly with the anteroinferior angle of the parietal bone (Figs. 6.11 and 6.14). The lesser wing articulates anteriorly with the orbital plate of the frontal bone. The lower part of the pterygoid process articulates, anteriorly, with the maxilla. The anterior margin of the medial pterygoid plate articulates with the perpendicular plate of the palatine bone. The pyramidal process of the palatine bone fits into the interval between the lower ends of the medial and lateral pterygoid plates. The vaginal plate (arising from the medial side of the pterygoid process) articulates anteriorly with the sphenoidal process of the palatine bone, and medially with the ala of the vomer (Fig. 6.22).

The Palatine Bones Each palatine bone is made up mainly of two plates, one perpendicular and the other horizontal (Figs. 6.6, 6.18, 6.21, 6.22, 6.24, 6.25,6.37, 6.38, 7.24). The horizontal plate forms the posterior part of the bony palate. Its lateral margin joins the lower end of the perpendicular plate. The perpendicular plate lies in the posterior part of the lateral wall of the nasal cavity. In addition to these two plates the palatine bone has three processes —pyramidal, orbital and sphenoidal.

The Horizontal Plate The horizontal plate has superior and inferior surfaces. The inferior surface has been examined when the anterior part of the skull was viewed from below (Figs. 6.6, 6.21, 6.25). Note that each horizontal plate meets the plate of the opposite side at the interpalatine suture. Anteriorly, it meets the palatine process of the maxilla. The posterior edge of the plate is free: it provides attachment to the soft palate. In the midline the posterior edges of the right and left horizontal

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plates project backwards to form the posterior nasal spine. A little in front of the posterior margin the inferior surface of the horizontal plate shows a raised palatine crest. The superior surface of the horizontal plate forms the floor of the posterior part of the nasal cavity. In the midline (where the two horizontal plates meet) there is an elevation called the nasal crest. This crest articulates

Fig. 7.24. Right palatine bone, posteromedial aspect.

with the vomer and contributes to the nasal septum.

The Perpendicular Plate The perpendicular plate of the palatine bone lies in the lateral wall of the nasal cavity (Figs. 6.19, 6.24, 6.37). Anteriorly, it articulates with the maxilla and posteriorly with the medial pterygoid plate. The perpendicular plate has medial and lateral surfaces. The lateral surface articulates with the maxilla converting the greater palatine groove on the latter into the greater palatine canal. The perpendicular plate overlaps the posterior part of the maxillary hiatus. Superiorly, it forms the medial wall of the pterygopalatine fossa. The medial surface of the perpendicular plate forms part of the lateral wall of the nasal cavity. Inferiorly, this surface has a conchal crest that gives attachment to the inferior nasal concha; and superiorly it has an ethmoidal crest to which the middle nasal concha is attached (Fig. 6.37). The upper border of the perpendicular plate has a notch which forms the lower part of the sphenopalatine foramen. (The foramen is bounded above by the body of the sphenoid) (Figs. 6.19, 6.37, 7.24).

The Pyramidal Process The pyramidal process of the palatine bone (Figs. 6.18, 6.21, 6.24, 6.25, 7.24) passes backwards and laterally from the posterolateral angle of the horizontal plate. It is wedged between the

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maxillary tuberosity (anteriorly) and the pterygoid process (posteriorly) and occupies the interval between the lower ends of the medial and lateral pterygoid plates. The lesser palatine foramina are seen on the inferior aspect of the pyramidal process.

The Orbital Process

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The orbital process of the palatine bone (Figs. 6.11, 7.24) arises from the anterosuperior angle of the perpendicular plate. It forms a small part of the floor of the orbit.

The Sphenoidal Process The sphenoidal process (Figs. 6.22, 7.24) arises from the posterosuperior angle of the perpendicular plate. It meets the vaginal plate of the sphenoid bone and helps to form the palatovaginal canal.

The Ethmoid Bone The ethmoid bone has a complicated configuration that is explained schematically in figure 6.42. It consists of a median vertical plate, and right and left labyrinths (Figs. 6.7-6.9, 6.11, 6.28, 6.38-6.40, 6.42). The median plate can be subdivided into a small part the crista galli which is seen in the floor of the anterior cranial fossa (Figs. 6.7, 6.28), and the perpendicular plate which forms a considerable part of the nasal septum (Fig. 6.39). The labyrinth consists of a number of ethmoidal air sinuses (Figs. 6.40, 6.42) that are enclosed in thin plates of bone. Laterally, the labyrinth is bounded by the orbital plate (which forms a considerable part of the medial wall of the orbit—Fig. 6.11) and medially it is bounded by the medial plate which lies in the lateral wall of the nasal cavity. Passing medially into the nasal cavity from the medial plate there are curved plates of bone that form the superior and middle nasal conchae (Figs.6.38, 6.42). Each labyrinth is connected to the median plate by a narrow horizontal plate that passes laterally from the junction of the crista galli with the perpendicular plate. This horizontal plate has numerous perforations and is, therefore, called the cribriform (= sieve like) plate. The cribriform plate forms part of the floor of the anterior cranial fossa and part of the roof of the nasal cavity (Figs. 6.7, 6.28).

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The walls of many ethmoidal air cells are incomplete. In the intact skull they are completed by parts of the maxilla and of the frontal, lacrimal, sphenoid and palatine bones. Articulations The perpendicular plate of the ethmoid articulates anteroinferiorly with the septal cartilage of the nose, posteroinferiorly with the vomer, anteriorly with the frontal and nasal bones, and posteriorly with the sphenoid (Fig. 6.39). The cribriform plate articulates laterally with the orbital plate of the frontal bone, and posteriorly with the sphenoid (rig. 6.28). The labyrinth articulates above with the frontal bone, posteriorly with the sphenoid, and laterally with the maxilla, the palatine bone and the lacrimal bone. The medial aspect of the labyrinth gives attachment to part of the inferior nasal concha.

Some small bones The Lacrimal Bones Each lacrimal bone is a small thin plate placed in relation to the anterior part of the medial wall of the orbit (Figs. 6.4, 6.37). It has a lateral surface, seen in the orbit; and a medial surface that helps to form the lateral wall of the nose. The lateral surface is marked by a vertical lacrimal crest in front of which there is a vertical groove. This groove meets a similar groove on the frontal process of the maxilla to form the groove for the lacrimal sac. Inferiorly, the lacrimal groove is continuous with the nasolacrimal canal. A descending process from the lacrimal bone helps to complete the medial wall of the canal (along with the lacrimal process of the inferior nasal concha). A curved spicule of bone called the lacrimal hamulus lies in the lateral wall of the upper end of the nasolacrimal canal. Articulations The lacrimal bone articulates, anteriorly, with the frontal process of the maxilla; posteriorly, with the ethmoid; superiorly, with the frontal bone; and inferiorly, with the maxilla.

The Nasal Bones The right and left nasal bones form the bridge of the nose (Figs. 6.4, 6.6, 6.8, 6.9, 6.21, 6.22, 6.39). Each bone articulates medially with the bone of the opposite side, laterally with the frontal process of the maxilla, and superiorly (and by its posterior surface) with the nasal part of the frontal bone. The inferior margin of the bone gives attachment to the lateral nasal cartilage.

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The posterior surface of the bone is grooved and takes part in forming the anterior part of the roof of the nasal cavity. The medial margins of the two nasal bones are thickened (on this aspect) and project into the nasal cavity as a crest which contributes to the nasal septum.

3 The Vomer The vomer is a flat plate of bone that forms the postero-inferior part of the nasal septum (Figs. 6.4, 6.6, 6.8, 6.9, 6.21, 6.22, 6.29). It articulates antero-superiorly with the perpendicular plate of the ethmoid. Postero-superiorly the vomer articulates with the body of the sphenoid. Here the vomer has two alae: the rostrum of the sphenoid fits into the interval between the alae. Inferiorly, the vomer is attached to the palatine processes of the maxillae, and to the horizontal plates of the palatine bones. Anteriorly, the vomer gives attachment to the septal cartilage of the nasal septum.

The Inferior Nasal Concha This is a thin curved plate of bone lying in relation to the lateral wall of the nasal cavity (Figs. 6.4, 6.8, 6.37, 6.38). The plate is free inferiorly. Its superior margin is attached to the maxilla (conchal crest) anteriorly, and to the conchal crest on the perpendicular plate of the palatine bone posteriorly. In between these it is attached to the lacrimal bone (through a lacrimal process), and along with the latter it forms the medial boundary of the nasolacrimal groove.

The Hyoid Bone The hyoid bone is not a part of the skull, but is considered here for sake of convenience. The hyoid bone is present in the front of the upper part of the neck. It is not attached to any other bone directly; but is held in place by muscles and ligaments which are attached to it. The most important of these are the stylohyoid ligaments by which it is suspended from the base of the skull. The bone consists of a central part called the body, and of two cornua — greater and lesser — on either side (Figs. 7.25 to 7.30). The body is roughly quadrilateral. It has an anterior surface directed forwards and upwards, and a posterior surface directed backwards and downwards. The anterior surface is divided into upper and lower parts by a transverse ridge, and into right and left halves by a median vertical ridge. The posterior surface is smooth.

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The greater cornua are attached to the lateral part of the body, from which they project backwards and laterally. They are flattened and have upper and lower surfaces; and medial and lateral borders. The posterior end of each cornu is enlarged to form a tubercle. The lesser cornua are small and conical. They project upwards and laterally from the junction of the body and the greater cornua. The union between the body and greater cornua is cartilaginous in the young, but they fuse in later life. The lesser cornua are attached by fibrous tissue (but sometimes there may be synovial joints between them and the greater cornua).

Fig. 7.25. Hyoid bone, seen from the front.

Attachments on the Hyoid Bone A. The muscles attached to the hyoid bone are as follows (Figs. 7.28 to 7.30)

Fig. 7.26. Hyoid bone, seen from the lateral side.

(a) The lowest fibres of the genioglossus are inserted into the upper border of the body. (b) The geniohyoid is inserted on the anterior surface of the body. (c) The mylohyoid is inserted on the anterior surface of the body below the insertion of the geniohyoid.

Fig. 7.27. Median section through the hyoid bone.

(d) The sternohyoid is inserted into the medial part of the inferior border of the body. (e) The superior belly of the omohyoid is attached to the lateral part of the inferior border of the body. (f) The middle constrictor of the pharynx arises from the upper surface of the greater cornu, and from the posterolateral aspect of the lesser cornu. (g) The hyoglossus arises from the upper surface of the greater cornu (lateral to the origin of the middle constrictor), and from the lateral part of the body. (h) The stylohyoid muscle is inserted into the upper surface of the greater cornu near its junction with the body.

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Fig. 7.28. Attachments on the hyoid bone, anterosuperior aspect. 3

(i) The thyrohyoid muscle is inserted into the anterior part of the lateral border of the greater cornu.

B. Other structures attached to the hyoid bone are as follows. (a) The stylohyoid ligament is attached to the apex of the lesser cornu. (b) The thyrohyoid membrane is attached to the medial border of the greater cornu, and to the upper border of the body.

Fig. 7.29. Schematic parasagittal section through the body of the hyoid bone, to show the arrangement of structures attached.

(c) The fibrous loop for the tendon of the digastric is attached to the lateral part of the upper surface of the greater cornu, behind the insertion of the stylohyoid muscle.

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Development and Ossification of the Hyoid Bone The upper half of the body, and the lesser cornua of the hyoid bone are derived from the cartilages of the second pharyngeal arches. The lower half of the body, and the greater cornua are derivatives of the cartilages of the third pharyngeal arches. The hyoid bone ossifies from six centres. One centre appears in each greater cornua towards the end of fetal life. Two centres appear in the body at about the time of birth. Two centres appear in the lesser cornua only at about the age of puberty.

Fig. 7.30. Schematic vertical section through a greater cornu of the hyoid bone to show the arrangement of structures attached.

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Index 3 Acetabulum, 62 Acromion, 14 Air cells, mastoid, 218 Angle sternal, 135 subpubic, 71 Annulus fibrosus, 119 Antrum, mastoid, 164, 218 Aperture nasal, anterior, 153 nasal, posterior, 170 Aponeurosis ,plantar, 308 Aquaeduct, of vestibule, 182, 218 Arch pubic, 62 superciliary, 152, 208 zygomatic, 161, 163, 216 vertebral, 113 Asterion, 162 Attachments. See individual bones

Bar, costotransverse, 117 intertubercular, 117 Bone. See individual names Border. See individual bones Bregma, 158

Calcaneus, 98 Canal adductor, 276 carotid, 175, 183, 187, 218 condylar, 215 condylar, anterior, 175 condylar, posterior, 175, 182, 189 ethmoidal, anterior, 185, 189 ethmoidal, posterior, 185, 190 hypoglossal, 175, 182, 183, 189, 215 infraorbital, 185, 205

Canal (continued) nasolacrimal, 185 optic, 157, 180, 183, 184, 222 palatinovaginal, 166, 171 pterygoid, 166 vertebral, 113 vomerovaginal, 171 Canaliculus mastoid, 175, 188, 218 tympanic, 175, 188, 218 Canalis innominatus, 174,187, 222 Capitate bone, 43 Capitulum, 20 Carpal bones, 36 Carpal tunnel, 45 Cartilage, costal, 143 Cavity glenoid, 14 nasal, 191 of skull, 143 Clavicle, 9 Clivus, 214, 221 Coccyx, 130 Column, vertebral, 113 Concha nasal, 225 nasal, inferior, 227 sphenoidal, 221 Condyle occipital, 175, 215 of humerus, 20 of tibia, 81 Cornua of hyoid bone, 228 sacral, 129 Costal element, 118 Cranium, 145

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Crest conchal, 205, 224 ethmoidal, 224 frontal, 179, 208 infratemporal, 165 intertrochanteric, 74 lacrimal, anterior, 152 nasal, 224 obturator, 61 occipital, external, 159 occipital, internal, 182, 214 palatine, 169, 224 sacral, 129 sphenoidal, 221 supinator, 32 supramastoid, 161 Crista galli, 179, 225 Cuboid bone, 101 Cuneiform bone intermediate, 102 lateral, 103 medial, 102

Disc, intervertebral, 113 Dorsal digital expansion, 262 Dorsum sellae, 180 Eminence arcuate, 181, 218 canine, 153 frontal, 152 iliopubic, 60 intercondylar, of tibia, 81 Ends. See individual bones Epicondyle of femur, 76 of humerus, 20 Ethmoid bone, 146, 153, 157, 179, 191, 194, 225

Femur, 72 Fibula, 88 Fissure squamotympanic, 174 orbital, inferior, 157 orbital, superior, 157, 180, 183, 184

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Fissure (continued) petrooccipital, 182 petrosquamous, 174 petrotympanic, 174 pterygomaxillary, 165, 172, 186 Fontanelles, 158, 197 Foot, skeleton of, 95 Foramen caecum, 179, 189, 208 emissary sphenoidal, 174,182, 187, 222 ethmoidal, 157 frontal, 153, 208 incisive, lateral, 169, 186 infraorbital, 153, 184 jugular, 175, 183, 188, 215, 218 lacerum, 174, 180, 187 magnum, 175, 182, 183, 189 mandibular, 199 mastoid, 161, 182, 186, 217 mental, 198 obturator, 62 ovale, 174, 182, 183, 187, 222 palatine, greater, 170, 186 palatine, lesser, 170 parietal, 158, 186, 211 rotundum, 166, 180, 183, 190, 222 sacral, anterior, 127 sacral, posterior, 128 sphenopalatine, 166, 186, 224 spinosum, 174, 182, 187, 222 stylomastoid, 175, 183, 189, 217, 219 supraorbital, 153, 184, 208 transversarium, 115 vertebral, 113 zygomaticofacial, 153, 185, 207 zygomaticotemporal, 161, 185, 207 Foramina. See individual bones Fossa acetabular, 62 canine, 153 condylar, 175, 215 coronoid, 21 cranial, anterior, 179 cranial, middle, 180 cranial, posterior, 182 digastric, 199 hypophyseal, 180 iliac, 59

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Fossa (continued) incisive, 153, 169, 198 infraspinous, 14 jugular, 175, 215, 218 lacrimal, 157, 210 malleolar, 90 mandibular, 174, 216, 217 olecranon, 21 pterygoid, 172 pterygopalatine, 165 radial, 21 scaphoid, 172 sublingual, 199 submandibular, 199 supraspinous, 14 temporal, 162 trochanteric, 73 trochlear, 157, 210 Fovea in head of femur, 72 pterygoid, 199 Frontal bone, 146, 151,156, 179, 194, 208

Glabella, 152 Groove carotid, 180 for greater palatine canal, 205 infraorbital, 157, 185, 205 lacrimal, 153, 157 mylohyoid, 199 nasolacrimal, 205 obturator, 61 radial, 20 Hamate bone, 44 Hamulus, lacrimal, 226 Hamulus, pterygoid, 173 Hand synovial sheaths of, 268 bones of, 36 Hiatus for greater petrosal nerve, 181, 218 for lesser petrosal nerve, 181, 218 maxillary, 205 sacral, 129 Hip bone, 56

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Humerus, 18 Hyoid bone, 227

Iliac crest, 57 Ilio-tibial tract, 270 Ilium, 57 Inferior nasal concha, 146, 153, 191, 227 Ischium, 61 Jugum sphenoidale, 180 Lacrimal bone, 146, 157, 226 Lambda, 158 Lamina, of vertebra, 113 Line anterior oblique, 26 arcuate, 60 gluteal, anterior, 59 gluteal, inferior, 59 iliac, gluteal, posterior, 58 intertrochanteric, 74 mylohyoid, 199 nuchal, highest, 159 nuchal, inferior, 159 nuchal, superior, 159 oblique, of mandible, 198 pectineal, 61 spiral, 74 temporal, 152, 161, 211 trapezoid, 9 Linea aspera, 74, 276 Linea terminalis, 68 Lingula, 199 Lunate bone, 39 Malleolus lateral, 88 medial, 84 Mandible, 145, 198 Manubrium, 134 Maxilla, 145, 152, 156, 169, 191, 194, 204 Meatus acoustic, external, 162 acoustic, internal, 182, 183, 190, 218

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Metacarpal bones, 45 fifth, 47 first, 46 fourth, 47 second, 46 third, 47 Metatarsal bones, 104 Muscle abductor digiti minimi, 254, 307 abductor hallucis, 307 abductor pollicis brevis, 254 abductor pollicis longus, 266 adductor brevis, 278 adductor hallucis, 311 adductor longus, 276 adductor magnus, 279 adductor pollicis, 255 anconeus, 264 anterior vertebral, 322 biceps brachii, 243 biceps femoris, 289 brachialis, 244 brachioradiais, 258 buccinator, 313 coccygeus, 334 coracobrachialis, 244 deltoid, 239 diaphragm, 328 erector spinae, 324 extensor carpi radialis brevis, 260 extensor carpi radialis longus, 259 extensor carpi ulnaris, 264 extensor digiti minimi, 263 extensor digitorum, 261 extensor digitorum brevis, 294 extensor digitorum longus, 293 extensor hallucis longus, 292 extensor indicis, 267 extensor pollicis brevis, 267 extensor pollicis longus, 266 external oblique of abdomen, 329 flexor carpi radialis, 247 flexor carpi ulnaris, 248 flexor digiti minimi, 254 flexor digiti minimi brevis, 310 flexor digitorum accessorius, 309 flexor digitorum brevis, 306 flexor digitorum longus, 303

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Muscle (continued) flexor digitorum profundus, 250 flexor digitorum superficialis, 249 flexor hallucis brevis, 310 flexor hallucis longus, 302 flexor pollicis brevis, 254 flexor pollicis longus, 252 gastrocnemius, 299 gemelli, 285 gluteus maximus, 280 gluteus medius, 282 gluteus minimus, 282 gracilis, 274 infrahyoid, 319 infraspinatus, 241 intercostal, 326 internal oblique, of abdomen, 330 interossei, 256, 311 dorsal of hand, 257 dorsal of foot, 312 of foot, 311 palmar, 256 plantar, 312 lateral vertebral, 321 latissimus dorsi, 237 levator ani, 334 levator scapular, 238 longus capitis, 322 longus colli, 322 lumbrical, of hand, 253 lumbricals, of foot, 309 masseter, 315 obliquus capitis inferior, 323 obliquus capitis superior, 323 obturator externus, 286 obturator internus, 284 omohyoid, 319 opponens digiti minimi, 255 opponens pollicis, 255 pectineus, 275 pectoralis major, 233 pectoralis minor, 234 peroneus brevis, 298 peroneus longus, 297 peroneus tertius, 295 piriformis, 283 plantaris, 300 platysma, 317

OSTEOLOGY

INDEX

Muscle (continued) popliteus, 301 pronator quadratus, 246 pronator teres, 246 psoas major, 269 psoas minor, 269 pterygoid, lateral, 315 pterygoid, medial, 315 quadratus femoris, 285 quadratus lumborum, 333 quadriceps femoris, 272 rectus abdominis, 332 rectus capitis anterior, 322 rectus capitis lateralis, 322 rectus capitis posterior major, 323 rectus capitis posterior minor, 323 rhomboideus major, 238 rhomboideus minor, 238 sartorius, 271 scalenus anterior, 321 scalenus medius, 321 scalenus minimus, 321 scalenus posterior, 321 semimembranosus, 288 semispinalis capitis, 325 semitendinosus, 287 serratus anterior, 235 soleus, 300 splenius capitis, 325 sternocleidomastoid, 318 sternocostalis, 327 sternohyoid, 319 sternothyroid, 319 subclavius, 234 subcostales, 327 subocipital, 323 subscapularis, 242 supinator, 265 supraspinatus, 240 temporalis, 314 tensor fasciae latae, 270 teres major, 242 thyrohyoid, 319 tibialis anterior, 291 tibialis posterior, 304 transversus abdominis, 331 trapezius, 236 triceps, 245

339

Nasal bone, 148, 152, 226 Nasion, 152 Navicular bone, 100 Notch acetabular, 62 clavicular, 134 fibular, 84 frontal, 153, 208 infraorbital, 184 intercondylar, of femur, 75 jugular, 135 mandibular, 198 mastoid, 175 sciatic, greater, 58, 61 spinoglenoid, 14 supraorbital, 153, 184, 208 suprasternal, 135 trochlear, 20, 30 ulnar, 27 vertebral, 115 Nucleus pulposus, 119 Occipital bone, 146, 159, 174, 213 Orbit, 156 apex of, 156 base of, 156 margins of, 156 walls of, 156 Ossification. See individual bones Palate, 169 Palatine bone, 169, 191,223 Parietal bone, 146, 158,161, 211 Patella, 79 Pecten pubis, 61 Pedicle, of vertebra, 113 Pelvis aperture of, inferior, 69 as a whole, 68 brim of, 68 diameters of, 69 false, 68 greater, 68 inlet of, 68 lesser, 68 sex differences in, 70 true, 68

3

340

Phalanges of fingers, 49 of foot, 107 Pisiform bone, 39 Plate articular, of tympanic, 174 cribriform, 179, 225 horizontal, of ethmoid, 225 horizontal, of palatine bone, 169, 223 medial, of ethmoid, 225 median, of ethmoid, 225 orbital, of ethmoid, 225 perpendicular of palatine, 170 perpendicular, of ethmoid, 225 perpendicular, of palatine bone, 224 pterygoid, lateral, 165, 173, 222 pterygoid, medial, 165, 172, 222 tympanic, 164, 219 vaginal, of sphenoid, 171 Premaxilla, 169 Process accessory, 118 alveolar, 153, 169, 198 articular of vertebra, 114 clinoid, anterior, 180 clinoid, posterior, 180 condylar, 198 coracoid, 14 coronoid, 30, 198 frontal, of maxilla, 206 jugular, 175 mamillary, 118 mastoid, 162, 217 olecranon, 30 orbital, of palatine bone, 225 palatine, of maxilla, 206 pterygoid, 165, 171, 222 pyramidal, 165, 169, 224 sphenoidal, of palatine bone, 170, 225 styloid, of skull, 162 of fibula, 88 of radius, 27 of ulna, 32 xiphoid, 134 zygomatic, of frontal bone, 208 zygomatic, of maxilla, 206 zygomatic, of temporal, 216

TEXTBOOK

OF

HUMAN

Promontory, sacral, 128 Protuberance mental, 200 occipital, external, 159 occipital, internal, 182, 214 Pterion, 161 Puboischial index, 71 Radius, 25 Retinaculum extensor, of ankle, 296 extensor, of wrist, 268 flexor, of ankle, 305 flexor, of wrist, 253 of wrist, flexor, 45 Ribs, 137 atypical, 139 false, 137 first, 139 floating, 137 second, 140 true, 137 twelfth, 141 Scaphoid bone, 38 Scapula, 12 Sella turcica, 180 Sheath, fibrous flexor, 308 Sinus tarsi, 98 Sinus, paranasal, 194 ethmoidal, 195 frontal, 194 maxillary, 194 sphenoidal, 194, 221 Skull as seen from above, 158 as seen from behind, 159 as seen from below, 169 as seen from lateral side, 160 as seen from the front, 151 base of, 145, 169 cap of, 145 cavity of, 145 general review, 145 vault of, 145 Space, intercostal, 137

OSTEOLOGY

INDEX

Sphenoid bone, 146, 148, 151, 157, 164, 171, 180, 184, 220 body of, 171 processes of, 171 rostrum of, 171 wings of, 171 Spine iliac, anterior inferior, 57 iliac, anterior superior, 57 iliac, posterior inferior, 58 iliac, posterior superior, 57 mental, 200 nasal, anterior, 153, 206 nasal, palatine, 169 of scapula, 14 of sphenoid, 174, 222 Sternebrae, 135 Sternum, 134 Sulcus calcanei, 98 chiasmaticus, 180 intertubercular, 18 preauricular, 60 sigmoid, 182 transverse, 182 Surface. See individual bones Sustentaculum tali, 98 Sutural bone, 159 Suture frontomaxillary, 151 frontonasal, 151 frontosphenoid, 160 frontozygomatic, 151 intermaxillary, 151, 169, 206 internasal, 151 interpalatine, 169 nasomaxillary, 151 occipito-mastoid, 159 palatomaxillary, 169, 206 parietomastoid, 159, 161 parietosphenoid, 160 parietosquamous, 161 squamomastoid, 162 zygomaticomaxillary, 151 Symphysis menti, 199 Synovial sheaths, 305 Talus, 99

341

Tegmen tympani, 174, 181, 218 Temporal bone, 148, 151, 161, 174, 180, 216 Tibia, 81 Tooth canine, 153 incisor, 153 molar, 153 premolar, 153 Trapezium, 41 Trapezoid bone, 42 Triangle, suprameatal, 164 Trigeminal impression, 180, 218 Triquetral bone, 40 Trochanter greater, 73 lesser, 73 Trochlea, 20 Tube, auditory, 174 Tuber, 158 frontal, 152, 208 parietal, 158, 211 Tubercle adductor, 76 articular, of temporal bone, 174, 217 calcaneal, anterior, 99 conoid, 9 deltoid, 9 genial, 200 infraglenoid, 14 jugular, 182, 215 mental, 198, 200 of atlas, 121 of humerus, 18 of iliac crest, 57 of rib, 137 of root of zygoma, 163 of talus, 100 of transverse process, 117 of trapezium, 41 peroneal, 98 pharyngeal, 175, 214 postglenoid, 163 quadrate, 74 spinous, 129 supraglenoid, 14 Tuberculum sellae, 180

3

342

Tuberosity calcaneal, 99 deltoid, 19 gluteal, 75 iliac, 60 ischial, 61 maxillary, 165, 169, 205 of cuboid bone, 101 of fifth metatarsal, 105 of navicular bone, 100 radial, 25 tibial, 81 ulnar, 30

TEXTBOOK

OF

HUMAN

cervical, 115 cervical,first, 121 cervical,second, 123 cervical,seventh, 125 lumbar, 115 lumbar, fifth, 126 thoracic, 115 thoracic, eleventh, 125 thoracic, first, 125 thoracic, tenth, 125 thoracic, twelfth, 125 typical, 113 Vertebral column, 113 Vomer, 146, 153, 170, 227

Ulna, 30 Xiphoid process, 134 Vertebra atlas, 121 axis, 123

Zygomatic bone, 146, 156, 163, 207

OSTEOLOGY