Anatomy of crocodiles Vethacking.com @ BVSc,UZ-ATV100 Revision notes
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Crocodiles are sturdy lizard-shaped aquatic reptiles of the order crocodilidae. There are 22 species crocodiles which are remarkably similar. Are subdivided into three families, Alligatoridae (the caimans, Caiman, Palaeosuchus, Melanosuchus, and alligators Alligator) Crocodylidae (‘true’ crocodiles, Crocodylus and dwarf crocodile Osteolaemus) Gavialidae (the Gharial Gavialis and False Gharial Tomistoma) There are two common species of crocodiles, the saltwater or estuarine crocodile, Crocodylus porosus and the freshwater freshwater crocodile, Crocodylus johnstoni .
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Introduction •
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With the birds, they are the only surviving archosaurs, the group which included the dinosaurs. These large amphibious and carnivorous reptiles inhabit tropical and subtropical lakes, rivers and coasts. They lay their eggs in nests constructed on land. Their morphology and physiology physiology have have been shaped by similar lifestyles, allowing many generalisations generalisations about the group of crocodilians as a whole
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Crocodilians C rocodyl rocodylus us porosus (Crocodylidae): the salt water crocodile shows pronounced sexual dimorphism, as seen in this male (left) and female resting on the shore. [G. Grigg]
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Crocodilians
Crocodylus porosus (Crocodylidae): when feeding in the water,, this species lifts the tail to counter balance the head [G. water Grigg]
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Crocodilians
Cr ocodyl ocodylus us porosus ( Cr ocodyl ocodylidae idae): ): the snout is broad and rounded,the teet teeth h (wellworn in this this old animal) animal) are are s et in an irr eg egula ularr row, and a palatal pala tal flap clos es the entrance to to the the throat
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Crocodilians
C rocodylus rocodyl us johns toni ni and (Crocodylidae): theto eyes the slit-like ears are set high on the head, and can be closed during diving;G.grigg
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Genera Generall morphology •
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Crocodilians are sturdy lizard-shaped reptiles, with a well-armoured head and trunk and with horny skin and scales, reinfo reinforced rced with bony plates In modern Crocodylia, Crocodylia, at least, the head is generally generally flattened flattened and the snout elongated. elongated. The nasal capsules lie near the tip of the snout, and nostrils which can close in the external nares tend to be raised above the tip of the snout; thus submerged crocodilians are inconspicuous when drifting driftin g toward terrestrial prey. Members of the Alligatoridae tend to have broad snouts, whereas those of the Crocodylidae range from broad to long and slender In gavialids the snout is extremely slender
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Generall morphology Genera •
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Crocodilians have laterally compressed compressed tails, webbed hind feet, and the nostrils, eyes and ears are placed high along the head he ad and snout, all consonant with aquatic habits. Skull and jaws are solid and together with the strong peg-like teeth can maintain an effective hold on prey. The palatal flap, a rigid plate of tissue at the rear of the oral cavity cavity,, closes the posterior buccal space (oesophagus and glottis) against the entry of water. water. A well-developed hard palate permits ventilation from nostril to glottis, bypassing the mouth
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Generall morphology Genera •
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The nostrils can be closed tightly during submergence. Adult crocodilians are large and species show an enormous size range. The smallest are species species of Palaeosuchus Palaeosuchus and Osteolaemu Osteolaemuss which grow to an adult size of 1 to 1.5 m. Males of Crocodylus porosus more than 7 m in length and weighing perhaps 2000 kg, are the largest of the extant reptiles. Crocodilians show a pronounced sexual dimorphism. Males grow larger often more rapidly than females, even though they attain sexual maturity at and an equivalent age Apart from size, there is no external indication of sex. The alimentary, urinary and reproductive systems open to the exterior via the midventral midven tral longitudinal slit of the cloaca.
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Integument •
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The skin is covered with keratinised scales, or scutes, many of which are reinforced reinfor ced with bony plates, or osteoderms. Osteoderms are most prevalent prevalent in the dorsal and nuchal scutes which commonly bear conspicuous ridges, and in the belly scales of some species. The nuchal, dorsal and some of the rectangular and keeled scutes are covered by hard, wear-resistant beta-keratin. Since they are vascularised, scutes are involved in thermoregulation The fieldsofofalpha-keratin scutes are embedded in the intermediate under a covering alpha-ker atin which provides an important skin barrier to water and electrolyte exchange. exchange. This facilitates the homeostasis homeostasis of body fluids f luids in a wide range of salinities (Salt and Water Water Regulation).
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Integument •
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Flexible skin covers the neck and the flanks, whereas the abdomen and sides of the tail are sheathed in large, flat, squarish scutes arranged neatly in rows. Crocodilian scales bear a pore that is generally thought to be sensory se nsory,, analogous to the lateral line of fishes. Higher densities of small scales around the head, particularly on the upper and lower jaws concentrate this supposed mechanosensory apparatus. Alternatively,, the pores could be a source of a detergent-like Alternatively detergent-like or oily substance (perhaps a modification of betakeratin) betakeratin) since mud seems to flush off them easily in the wild.
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Integument •
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The prominent paired gular and paracloacal integumentary integumentary glands are everted at capture. The gular glands lie in ventral folds of skin at the angles of the jaw and the paracloacal glands are embedded in i n the lateral walls of the cloaca. Their holocrine secretions are primarily lipid. Secretions analysed from both pairs of glands in most crocodilian species contain sterols, free fatty acids, triglycerides, steryl esters and aliphatic alcohols and, commonly, hydrocarbons
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Muscular system •
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The crocodilian muscles seem to follow the general tetrapod pattern The crocodilian muscles reflect the general short fibre phenomenon Jaw closing muscles appear to be much more massive than the openers and the jaws of even of medium-sized specimens can be held shut comparatively compara tively easily, easily, especially when coupled with the leverage attainable by grasping the snout. Much of aquatic propulsion depends on the axial musculature. However, associatedterrestrial girdles. locomotion is effected by the muscles of limbs and the Some ventilation is powered by the intercostals, but much of inhalation reflects the contraction of the m. diaphragmaticus, a striated muscle that connects the liver to the pelvic girdle
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Muscular system •
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The muscles muscles deltoideus deltoideus clavicul clavicularis, aris, scapuloh scapulohumer umeralis alis caudalis caudalis and teres major all lie together on the lateral surface of the scapula blade. Muscles are divided into groups. Forelimb muscles are split into extrinsic/intrinsic and forearm pronators/supinators. Intrinsic muscles arewrist further split into extensor/flexor extensor/flexor muscles of the shoulder, elbow and Hindlimb muscles are divided into superficial/deep and then dorsal/ventral groups
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Muscular system Fig 1. Orientation terminology used in muscle description. Diagram of the Crocodylus porosus hindlimb with terms used to describe orientation.
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Muscular system •
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The large superficial dorsal muscles of the forelimb are often removed during the skinning process . It is therefore therefore not possible to identify identify or model these muscles. These include the trapezius, latissimus dorsi, rhomboideus and serratus ventralis cervicus. In the lower limbs, where muscles inserting into the manus and pes are alsobe severed during skinning thus three muscles in the hindlimb cannot identified. quadratus and These include the flexor flexor digitorum brevis, pronator quadratus extensor hallucis longus.
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Forelimb muscles •
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Superficial extrinsic muscles . Pectora Pect oralis lis (PEC) This muscle originates by a fleshy attachment along the ventral midline of the animal from the interclavicle interclavicle and sternal ribs. It inserts by a tendon on the proximo-ventral humerus at the deltopectoral crest. Its principle function is in shoulder and limb adduction. It is a very large sheet-like muscle that covers covers the entire superficial ventral chest area. Deep extrinsic muscles Levatorr scapulae (LS) (collo-scapularis Levato (collo-scapularis supericialis )
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Forelimb muscles •
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This muscle's origin lies with the neck muscles on the lateral cervical ribs. It inserts on the anterior border of the scapula by a fleshy attachment which extends from from the most anterodistal anterodistal part of the scapula to to the glenohumeral joint and is largely obscured from view by the trapezius which overlies this part of the LS . It plays a major part in drawing the shoulder anteriorly. anteriorly.
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Forelimb muscles •
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Serratus ventralis ventralis thoracis thoracis (serratus posterior posterior ; thoracic-scapularis thoracic-scapularis superficialis) This muscle originates from the trunk at the ventro-lateral ventro-lateral ribs. It inserts by a tendon on the entire medio-posterior margin of the scapula. It is a broad but thin muscle involved in extension of the pectoral girdle. Costoco Cost ocorac racoideus oideus prof profundus undus This muscle originates in the trunk on the lateral lateral margin of the first few ribs and inserts at the ventro-posterior margin of the corac coracoid. oid. Both attachment points are fleshy. This muscle is long but thin and lies deep to the pectoralis. It functions as a pectoral girdle extensor.
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Fig 3. Fresh-tissue dissection with muscles identified around shoulder. Lateral view of right shoulder region of Crocodylus porosus poros us (XCb (XCb Cp5). TM: Teres major, DS: Deltoideus scapularis, SHC: Scapulo Scapulohumer humeralis alis caudali caudalis, s, DC: Deltoideus clavicularis, CBD: Coracobrachialiss brevis Coracobrachiali dorsalis, TLM: Triceps longus medialis, TLL: Triceps longus lateralis, TB1: Triceps brevis 1.
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Fig 4. Fresh-tissue dissection with some hindlimb muscles identified. Dorsolateral view of right hindlimb of Crocodylus porosus. FTE: flexor tibialis externus, IT1-3: Iliotibialis 1±3, IF: Iliofemoralis, FMTE: Femorotibialis Femorotibia lis externus, GE: Gastrocnemius externus, PP: Pronator profundus, FB: Fibularis brevis, TA: Tibialis anterior .
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Muscular system
Fig 5. Three-dimensional model of forelimb musculature in Crocodylus porosus . Lateral view of the
right forelimb.
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Fig 6. Superficial extrinsic muscles of the forelimb. PEC: Pectoralis.
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Muscular system
capulae e, SVT: S err erratus atus ventralis v entralis thor thoraci aciss , Fig 7. Deep extrinsic muscles of the forelimb. LS: Levator s capula COCS: C os osto tocora coracoideu coideuss s upe uperfic rficial ialis is , COCP: Costocoracoideus profundus .
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Intrinsic muscles
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Shoulder extensors/flexors. extensors/flexors.T Teres major (TM)
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This muscle originates on the disto-lateral disto-lateral surface of the scapula by a fleshy attachment, attachment, and inserts via a long lo ng and well-defined tendon onto a bony ridge on the proximo-lat proximo-lateral eral humerus. TMthe makes up thedorsi. postero-lateral postero-lateral surface of the scapula and lies deep to latissimus It is involved in shoulder abduction, and also flexion to a minor degree.
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Deltoideus Delto ideus scapularis scapularis (DS) (scapular (scapular triceps triceps )
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This muscle originates by a fleshy attachment on the disto-lateral scapula and inserts by a tendon on o n the dorso-lateral humeral head. It is an elongate muscle that attaches to the scapula along its length from point of origin until it becomes tendinous.
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It lies anterior to teres major.
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The DS acts as a shoulder abductor and flexor.
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Fig 8. Intrinsic muscles of the forelimb: shoulder extensors and flexors. TM: Teres major , DS: Deltoideus scapularis, SHC: Scapulohumeralis caudalis, DC: Deltoideus clavicularis, CBV: Coracobrachialis brevis ventralis, SC:
Supracoracoideus, CBD:
Coracobrachialis brevis dorsalis.
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Supracoracoi Supracor acoideus deus (SC) This muscle originates at the proximo-lateral coracoid by a fleshy attachmentt and covers attachmen covers the entire humeral head. It inserts on the ventro-lateral ventro-lateral humerus on the deltopectoral deltopectoral crest by a fleshy attachment. attachment. The SC is very broad and triangular in shape, making up much of the shoulder. It acts as a shoulder extensor and, to a minor degree, adductor. adductor. Scapulohume Scapu lohumeral ralis is cauda caudalis lis (SHC) (tere (teress minor minor ) This muscle originates on the proximo-later proximo-lateral al and posterior scapula, and inserts on the proximo-lateral proximo-lateral humeral head.
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Both attachments are fleshy. It is a small muscle that is largely overlain by teres major posteriorly and deltoideus scapularis anteriorly. anteriorly. The SHC functions as a shoulder abductor. abductor. Coracobrachialis Coracobr achialis brevis ventralis (CBV) This muscle originates by a fleshy attachment over the entire lateral corac coracoid crest.oid and inserts, also by a fleshy attachment, onto the deltopectoral It lies deep to the pectoralis and posterior to the biceps brachii. brachii. It is a large and broad muscle that cover coverss the lateral coracoid coracoid and proximo-ventral proximo-ventral humerus.
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The CBV acts as a shoulder and limb adductor. adductor.
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Coracobrachialis Coracobr achialis brevis dorsalis (CBD)
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This muscle originates from the antero-lateral antero-lateral and proximal scapula by a fleshy attachment.
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It inserts on the proximal third third of the anterior humerus near ne ar the
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deltopectoral deltopecto ral crest. crest. This muscle is triangular in shape and makes up much of the bulk of the shoulder along with the supracoracoideus. supracoracoideus.
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It acts as a shoulder extensor and possibly also as a joint stabiliser
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Subscapularis (SS) This muscle originates on the postero-lateral scapula by a fleshy attachmen attachment t and inserts by a fleshy attachment on the dorso-lateral humeral head. It is a shoulder extensor and has also been identified as a shoulder stabiliser due to its small size and limited mechanical m echanical advantage Deltoideus clavicularis (DC) (scapular deltoid ) This muscle originates by a fleshy attachment on the antero-lateral scapula and inserts on the dorso-lateral head of the humerus, again by a fleshy attachment.
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It makes up much of the bulk of the shoulder along with the supracoracoideus, supracor acoideus, overlying most of coracobrachialis coracobrachialis brevis dorsalis
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as well as the insertion of deltoideus scapularis. It can sometimes be difficult to differentiate differentiate from coracobrachialis coracobrachialis brevis dorsalis and supracor supracoracoideus. acoideus.
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The DC acts to extend the shoulder.
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Elbow extensors/flexors Humerora Humer oradialis dialis (HR) (brachio-r (brachio-radiali adialiss ) This muscle originates on the ventro-lateral ventro-lateral humerus at the deltopectoral crest by a fleshy attachment. attachment. It inserts with biceps brachii and brachialis on the proximo-medial radius by a short tendon. The HR lies anterior to the biceps brachii and brachialis; it is also broader than these other two muscles. It functions to flex the elbow. elbow. Biceps brachii (BB) (coracoantebrachialis) (coracoantebrachialis)
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Fig 9. Intrinsic muscles of the forelimb: elbow extensors and flexors. TLL: Triceps longus longus lateralis , TLM:
Triceps lo Triceps longus ngus medialis , ABR: A bductor radialis r adialis , BB: B iceps brachii brachii , BR: Brachialis , HR: Humeroradialis , TB1-2: Tricep Tricepss brevis 1±2.
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This muscle originates on the ventral coracoid by a very long tendon (half the length of the muscle belly). It inserts by a tendon onto the proximo-medial radius. This muscle is rather slender and is a major elbow flexor. flexor.
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Brachialis (BR) This muscle originates by a fleshy attachment on the anterior humeral head. It inserts onto the proximo-medial radius with the tendon of the biceps brachii. The BR is a thin and elongate muscle that attaches attaches to the humerus along its length. It lies between the biceps brachii and the humeroradialis. It is involved in elbow flexion. Triceps longus longus lateral lateralis is (TLL) (anconeu (anconeuss scapularis scapularis )
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This muscle originates at the proximo-lateral proximo-lateral scapula via a tendon, superficial to the teres major and scapulohumeralis scapulohumeralis caudalis, but deep to deltoideus scapularis. It inserts by a tendon onto the lateral olecranon process of the proximal ulna. It makes up much of the dorsal surface of the upper arm and extends over the medial surface of triceps brevis 1.
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This muscle's primary function is in elbow extension.
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Triceps longus medialis (TLM) (anconeus scapulocorac scapulocoracoideus) oideus)
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This muscle originates by a tendon from the postero-lateral postero-lateral and proximal surface surface of the scapula, deep to the teres major major,, and inserts by a tendon on the olecranon process of the proximal proximal ulna with the triceps longus later l ateralis. alis. TLM lies posterior to the triceps longus lateralis lateralis and is of a similar size size and shape. It is an elbow extensor. Triceps brevis (TB) (TB1 (TB1 = Anconeus humeralis lateralis, TB2 = anconeus ancon eus humeralis humeralis medial medials, s, TB3 = anconeus anconeus major ) This muscle is composed of 3 parts.
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TB1 originates by a fleshy attachment attachment on the proximolater proximolateral al humerus, overlying the insertion of teres major.
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It inserts to bythe a tendon tendon on the proximal proximal at the olecranon olecranon process and attaches humerus for part of its ulna length. TB2 originates on the postero postero-dorsal -dorsal and proximal humerus, while TB3 originates on the posterior humeral head.
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TB2 and TB3 insert together with TB1 also by a tendinous attachmen attachment. t. TB2 and TB3 run postero-dorsally postero-dorsally along the humerus and sit flush against the bone, attaching along the length of the muscle. TB1 overlies much of TB2. All parts of this muscle are involved in elbow extension.
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Fig 10. Intrinsic muscles of the forelimb: wrist extensors/flexors. FUL: Flexor ulnaris longus, ECU: Extensor carpi ulnaris, ECRB: Extensor carpi radialis brevis, ECRL: Extensor carpi radialis longus, FDL1-2: Flexor digitorum longus, FCU: Flexor carpi ulnaris.
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Abductor radialis (ABR) (humero-radialis internus)
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This muscle originates by a tendon from the disto-lateral humerus
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and inserts by a fleshy attachment on the distal lateral radius. It runs along the lateral surface of the radius and attaches along its length.
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It lies between the extensor carpi radialis longus and extensor carpi radialis brevis. The ABR is an elbow flexor.
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Muscular system •
Wrist extensors/flexors .
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Flexor carpi ulnaris (FCU) (humero-radiali ( humero-radialiss lateralis)
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This muscle originates via a tendon at the disto-medial humerus and inserts by a fleshy attachmen attachmentt at the ventral manus.
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It lies medial to flexor digitorum longus 1 and is a relatively slender
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muscle. It is one of the major wrist flexors. flexors.
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Flexor digitorum longus (FDL) (flexor digitorum communis profundus )
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This muscle is composed of 2 parts. FDL1 originates on the ventro-medial and distal humerus via a tendinous attachment and inserts by a tendinous attachment into the manus at digit 2 with FDL2. It lies between flexor carpi ulnaris medially and pronator teres laterally,, and is a relatively thin muscle. laterally FDL2 originates by a fleshy fle shy attachment attachment at the proximo-medial head of the ulna before inserting via a tendon into the manus on the ventral surface of digits 1-3.
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FDL2 attaches to the ulna along its length. It is a thin muscle at its origin point but broadens substantially at the distal ulna before thinning again and becoming tendinous. Both parts of this muscle are involved in wrist flexion. Extensor carpi radialis longus (ECRL) (extensor carpi radialis ) This muscle originates on the ventro-lateral ventro-lateral humerus by a tendinous attachmentt and inserts, also by a tendon, on the dorsal manus. attachmen It is a long and relatively thin muscle that lies anterior to the abductor radialis. The ECRL functions as a wrist extensor Extensor carpi radialis brevis (ECRB) (extensor ( extensor carpi radialis profundus ; supinator manus)
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This muscle originates with two heads which are almost indistinguishable, one on the antero-proximal antero-proximal head of the ulna and
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the other on the poster-proximal radius, both by fleshy attachments. ECRB then inserts at the dorsal manus via a tendon.
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The origin of this muscle
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lies deep to the extensor carpus ulnaris and abductor radialis. It is involved in wrist extension.
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Extensor carpi ulnaris (ECU) ( ECU) (humero-carpi (humero-carpi ulnaris ; ectepicondylo-ulnaris ) This muscle originates by a tendon on the disto-ventral humerus at the lateral condyle and inserts at the dorsal manus via a tendon. It acts as an elbow flexor and wrist extensor.
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Flexor ulnaris longus (FUL) (humerodorsalis )
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This muscle originates at the disto-lateral humerus via a tendinous attachment.
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It runs along the lateral ulna and inserts by a tendon onto the dorsal metacarpals.
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This muscle is wider at origin and thins towards towards its insertion point.
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It lies posterior to the extensor carpi ulnaris.
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The FUL functions as an elbow flexor and wrist extensor.
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This muscle originates by a tendinous attachment at the ventro-distal humerus and inserts by a fleshy attachmen attachmentt on the ventral carpals. It attaches to the antero-medial radius along its length and lies between supinator anteriorly and flexor digitorum longus 1 posteriorly. Its principal function is in wrist pronation.
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Pronator quadratus (PQ)
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This muscle originates by a fleshy attachment at the proximo-medial ulna and inserts on the postero-distal radius. PQ is very broad at origin but thins towards its insertion point.
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It lies deep to the other ventral muscles of the forearm, between the
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radius and ulna. It is an elbow pronator and also assists in stabilising the radius and ulna.
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Supinator (SUP)
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This muscle originates by a tendinous attachment at the disto-lateral humerus and runs along al ong the lateral radius, radius, attaching to the bone, inserting by a tendon on the antero-distal antero-distal radius. It partially overlies extensor carpi radialis longus at origin.
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SUP is a large muscle that lies on the anterior edge of the radius.
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It acts as the major wrist supinator.
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Fig 11. Intrinsic muscles of the forelimb: pronators and supina sup inator tors s of the forearm. PQ: Pronator
,nator , quadratus upinator SUP: S upi PT: Pronator teres .
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Fig 12. Three-dimensional model of hindlimb musculature in C rocod rocodylu yluss po poros rosus us . Lateral view of the right hindlimb. The interactive version of this model is available in `Supplementary
Information'.
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Muscul Muscular ar sys system tem-- Hindl Hindlimb imb muscle muscless •
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Superficial dorsal muscles of the upper hindlimb. Iliotibialis (IT) (extensor iliotibialis) This muscle is made up of 3 parts. IT1 originates by a fleshy attachment from the antero-later antero-lateral al ilium and inserts via a tendinous attachment attachment to the proximo-anterior tibia, inserting with IT2 and IT3. It is a relatively slender muscle. IT2 originates by a tendon from the central lateral ilium between IT1 and IT3.
It inserts on the proximo anterior anterior tibia via a tendinous attachment. attachment.
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Muscul Muscular ar sys system tem-- Hindl Hindlimb imb muscle muscless •
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It is a sheet-like sheet-like muscle and is the largest of the iliotibialis muscles, making up almost the complete dorsolateral dorsolateral face of the thigh. It is broad at the proximal end, thinning and narrowing towards towards its insertion. IT3 originates by a fleshy attachmen attachmentt on the postero-lateral postero-lateral ilium and inserts on the proximo p roximo-anterior -anterior tibia with IT2, also by a tendon. It lies directly posterior to IT2 and anterior of flexor tibialis externus. It is of a similar shape to IT1. The iliotibialis muscles make make up the entire of the superficial dor dorso-latera so-laterall thigh are all used in extension of the knee.
Flexor tibialis externus (FTE)
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Hindlimb muscles •
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This muscle originates by a tendon from the postero-lateral postero-lateral ilium, posterior to iliotibialis 3, and inserts via a long tendon, shared with gastrocnemius externus, into the pes. gastrocnemius The muscle body extends to the insertion inse rtion of the flexor tibialis internus muscles at the knee, beyond that the tendon continues by stretching stretc hing medial to the gastrocnemius externus to the final insertion point at the proximal pes. The FTE is a large muscle that covers the posterior surface of the thigh and acts as a hip extensor and knee flexor.
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Hindlimb muscles
, FTE: Flexor tibialis tibialis exte externus rnus , ig 13. Superficial dorsal muscles of the upper hindlimb. ILFB: Iliofibularis
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Iliofib Ili ofibula ularis ris (IL (ILFB) FB)
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This muscle originates by a fleshy attachment at the central lateral ilium ventra ventrall to the origin of iliotibialis iliotibialis 3. It inserts on o n the proximo-lateral proximo-lateral fibula via a tendinous attachment.
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The distal part of the muscle belly is visible between iliotibialis 3 and
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flexor tibialis externus. It is a thin muscle that acts as a hip extensor and knee flexor flexor..
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Superficial ventral muscles of the upper hindlimb .
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Ambien Amb ienss (AM (AMB) B) (pubofe (pubofemor morali alis; s; sartoriu sartoriuss )
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Hindlimb muscles •
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This muscle originates on the proximo-lateral proximo-lateral pubis by a tendinous attachment. It inserts on the proximo-anterior proximo-anterior tibia at the cnemial crest via a long tendon.
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This muscle is wide at origin, thinning as it becomes tendinous for
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insertion. It is visible along the anterior surface of the thigh.
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Only a single head was identified in C. porosus.
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It is a knee extensor and hip flexor.
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Hindlimb muscles •
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This muscle originates on the proximo-lateral proximo-lateral pubis by a tendinous attachment. It inserts on the proximo-anterior proximo-anterior tibia at the cnemial crest via a long tendon.
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This muscle is wide at origin, thinning as it becomes tendinous for
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insertion. It is visible along the anterior surface of the thigh.
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Only a single head was identified in C. porosus.
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It is a knee extensor and hip flexor.
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Flexor tibialis internus (FTI) This muscle is composed of 4 parts. FTI1 originates from the postero-lateral postero-lateral ischium and inserts on the proximo-medial proximo -medial tibia via a long tendon with pubo-ischio-tibialis. It is a long and thin muscle. FTI2 originates by a fleshy attac attachment hment on the th e postero-ventral postero-ventral ilium and inserts on the proximo-medial tibia via a tendon with FTI1. It is the largest of the 4 parts and is broad. FTI3 originates on the proximo-lateral proximo-lateral ischium and inserts by a tendon on the proximo-medial tibia with the other FTI muscles.
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Hindlimb muscles Fig 14. Superficial ventral muscles of the upper hindlimb. AMB: A mbiens , PIT:
Pubo-ischio-tibialis, FTI13: Flexor tibialis tibialis internus 1± 1±3 3.
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It is broader than FTI1 and lies l ies ventral to the secondary tendon of the caudofem caudo femora oralis lis longus. FTI4 originates on the latero-ventral latero-ventral ilium near the ischium and inserts via a tendon with the other three FTI muscles. It is a small thin muscle. The FTI muscles are involved in hip extension and knee flexion.
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Pubo-ischio-tibialis (PIT) This muscle originates by a tendon at the postero-lateral ischium near where the ischium and pubis join, and inserts by a tendon on the proximo-medial tibia. It is a long and relatively thin muscle that lies lateral to flexor tibialis internus 1. Its origin also lies between pubo-ischiofemoralis externus 3 and adductor 1. The PIT is involved in hip extension and knee flexion; it also functions as an adductor to a minor degree.
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Deep dorsal muscles of the upper hindlimb. Iliofemoralis Iliofemor alis (IF) (caudali-iliofemor (caudali-iliofemoralis) alis) This muscle originates deep to iliotibialis 2 on the central lateral ilium via a tendinous attachment. It inserts by a fleshy attachment onto the distal third of the dorsolateral femur between between femorotibialis femorotibialis internus and femorotibialis femorotibialis externus. The IF is tear shaped and attaches along most of the length of the femur.
It is one of the hip abductor muscles.
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Femorotibialis internus (FMTI) This muscle originates by a tendon on the dorso-proximal femur, femur, distal and anterior to iliofemoralis. iliofemoralis. It then inserts on the cnemial crest via a tendon with femorotibialis externus. FMTI attaches to the femur and envelops the dorso-lateral dorso-lateral portion of this bone. It is involved in knee extension. Femorotibialis externus (FMTE) This muscle originates by a fleshy attachment approximately approximately one third of
the way down the dorsal femur.
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It inserts on o n the proximo-lateral proximo-lateral cnemial crest by a small tendon. FMTE merges with femorotibialis femorotibialis internus by a tendon at its insertion point but is separated at origin by the iliofemoralis. It lies posterior posterior to femorotibialis femorotibialis internus and is smaller than this muscle.
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It functions as a knee extensor. Deep ventral muscles of the upper hindlimb.
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Caudofemor Caudof emoralis alis longus (CFL) (coc (coccyg cygeoeo- fem femora oralis lis longus ; caudi caudi--
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femoralis
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Fig 15. Deep dorsal muscles of the upper hindlimb. FMTE: Femor Femorotibialis otibialis externus, IF: Iliofemoralis, FMTI: Femorotibialis internus.
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Fig 16. Deep ventral muscles of the upper hindlimb. CFL: Caudofemoralis Caudofemoralis longus, CFB: Caudofemoralis Caudofemoralis brevis, PIFI1-2: Pubo-ischio-femoralis Pubo-ischio-femoralis internus 1-2, ADD 1-2: Adductor 1-2, PIFE 2-3: Pubo-ischiofemoralis externus 2-3.
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Hindlimb muscles •
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This muscle originates by a fleshy attachment in the tail at numerous caudal vertebral haemal arches beginning at caudal vertebra 12. It inserts via a very large large tendon on the proximoventr proximoventral al femur at the fourth trochanter. trochanter. This muscle also has an accessory tendon that attaches at the ventrodistal femur on the tibial condyle with the gastrocnemius externus. This accessory tendon is covered in dorsal view by iliotibialis 3 and flexor tibialis externus.
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Hindlimb muscles •
The proximal third of this muscle, between its origin and insertion points, sits free from the caudal vertebrae and is the theref refore ore constrained by the hypaxial musculature, namely the transverse constrained transverse perenei, and also a layer of fat that separates the CFL from the hypaxial muscles.
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CFL is the largest muscle in the crocodile's body and performs the majority of the hip extension extension along with caudof caudofemoralis emoralis brevis.
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Caudofemoralis Caudofemor alis brev brevis is (CFB) (coccygeo-f (coccygeo-femor emoralis alis bre brevis vis ; caud caudiifem emor oral alis is ) This muscle originates in the tail by two heads, one from the posterolateral ilium and the other to caudal vertebrae 4 and 5, anterior to the origin of caudof caudofemor emoralis alis longus. It inserts by a tendon at the proximo-ventral proximo-ventral femur on the fourth trochanter. It lies antero-medial antero-medial to the caudofemoralis caudofemoralis longus and is the smaller of the two major hip extensors. Adductor (ADD) (adductor femoris femoris ; ischio-femora ischio-femoralis lis )
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This muscle is composed of 2 parts. ADD1 originates by a fleshy attachment at the ventrolateral ventrolateral surface of the ischium and inserts via a tendon at the at the ventro-medial femur. ADD2 lies posterior to ADD1. It also originates by a fleshy attachment on the ventro-later ventro-lateral al ischium and inserts on the disto-ventral femur again by a fleshy attachment. It is much longer and thinner than ADD1. The adductor is important for hip adduction and also contributes to extension of the hip joint.
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Pubo-ischio-fem Pubo-ischiofemoral oralis is ext externus ernus (PIFE) This muscle is composed of 3 parts. PIFE1 originates on the anterior boarder of the pubis, anterior to PIFE2, by a fleshy attachment. It inserts on the proximo-anterior proximo-anterior femur with the other two parts of PIFE. PIFE2 originates from the entire lateral lateral pubis and inserts via a tendon at the proximo-anterior femur. It is a fan-shaped muscle. PIFE3 originates by a fleshy attachment on the antero-lateral antero-lateral margin of the ventral ischium and inserts by a tendon on the proximo-anterior proximo-anterior femur with PIFE2.
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Hindlimb muscles •
It is less broad than PIFE2 PIFE 2 but is thicker. thicker. PIFE functions as a hip adductor and also function as a hip adductor adductor..
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Pubo-ischio-femoralis internus (PIFI) (quadratus lumborum)
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This muscle is composed of 2 parts.
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PIFI1 originates on the medial ilium and pro proximomedial ximomedial ischium by a fleshy attachment, and inserts on o n the proximal femur, femur, medial to the fourth trochanter trochanter and between the insertion of pubo-ischio-femoralis externus 3 and adductor 1.
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It is a short but thick muscle. PIFI2 originates anterior to the pelvic pe lvic girdle by a fleshy attachment on the transverse transverse processes of the few vertebrae anterior to the girdle. It inserts by a tendon onto the proximo-lat proximo-lateral eral femur near the fourth trochanter. It is a fan-shaped muscle. PIFI1 acts as a hip adductor while PIFI2 acts to both abduct and flex the hip.
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Hindlimb muscles •
It also function as a hip adductor function, as in PIFI1, rather than abduction .
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Superficial dorsal muscles of the lower l ower hindlimb.
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Gastrocnemius externus (GE)
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This muscle originates by a fleshy attachment at the caudofemoralis
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longus tendon on the postero-distal femur. It inserts by a wide tendon onto the lateral calcaneus.
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Hindlimb muscles •
It is a sizeable muscle, making up a large portion of the postero-later postero-lateral al lower limb.
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It is largely responsible for extension of the knee.
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Tibialis anterior (T (TA) A) (tibialis anticus)
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This muscle originates via a fleshy attachment on the antero-proximal
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tibia. Insertion is by a tendon into the dorsal surface of digits 2 and 3.
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It is a large and elongate muscle covering the anterior tibia and is
involved in ankle flexion.
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Hindlimb muscles •
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Fibularis longus (FL) This muscle's origin is on the proximo-medial tibia by a tendon and it inserts by a tendon at the astragalus. astragalus.
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The FL lies postero-medial to tibialis anterior. anterior.
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It acts to flex the ankle.
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Fig 17. Superficial dorsal muscles of the lower
hindlimb. GE:Gastrocnemius GE:Gastrocnemius exter externus, nus, TA: TA: Tibialis anterior, FL: Fibularis longus.
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Fig 18. Superficial ventral muscles of the lower hindlimb. GI: Gastrocnemius internus, EDL: Extensor digitorum longus, EDB: Extensor digitorum brevis.
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Hindlimb muscles •
Superficial ventral muscles of the lower hindlimb .
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Extensor digitorum longus (EDL) (extensor digiti )
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This muscle originates as a narrow tendon on the lateral fibul fibula, a, and inserts onto the dorsal surface of the digits via a tendinous attachment.
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It lies postero-lateral to tibialis anterior. The EDL is involved in ankle extension.
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It also functions as a digit extensor. extensor.
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Extensor digitorum brevis (EDB) (peroneus posterior ) This muscle originates by a fleshy attachment at the latero-distal fibula and inserts into the at digit It is a small but dorsal broad pes muscle and5. lies distal and posterior to the extensor digitorum digit orum longus longus and fibularis brev brevis. is. EDB functions to extend the pes. Gastrocnemius internus (GI) This muscle originates by a tendon from f rom the proximo-medial tibia and inserts at the ventral calcaneus by a tendon with the gastrocnemius externus. It is wide but thin thi n and lies deep to the gastr gastrocnemius ocnemius externus. GI is one of
the ankle extensors. extensors.
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Fig 19. Deep dorsal muscles of the lower hindlimb. FDL: Flexor digitorum longus, FHL: Flexor hallucis longus, PP: Pronat Pronator or profundus.
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Deep dorsal muscles of the lower hindlimb. Flexor digitorum longus (FDL) This muscle originates by a into tendon the ventro-later ventro-lateral al femur at the lateral condyle and inserts the on ventral pes by a tendon. This muscle is long and wide but quite thin. It lies directly over the flexor hallucis longus and is a knee extensor and also a digit flexor. Flexor hallucis longus (FHL) (tibialis posticus ) This muscle originates by a fleshy attachment from the lateral condyle of the femur and inserts by a tendon past the knee and into the ventral pes.
It is wide at the proximal end and tapers towards insertion.
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It covers much of the postero-ventral postero-ventral fibula and functions to extend the knee and flex the digits. Pronator profundus (PP) This muscle originates from the disto-lateral fibula via a fleshy attachment. It inserts at the tarsals, again by a fleshy attachment. PP is a small and almost spherical muscle on the disto-lateral disto-lateral fibula. It is involved in ankle extension, while its ability to pronate the ankle seems to be limited by its small s mall size.
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Deep ventral muscles of the lower hindlimb.
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Hindlimb muscles •
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Fibularis brevis (FB) (peroneus anterior ) This muscle originates on the lateral fibula by a fleshy attachmen attachmentt and inserts via a tendon on the dorsal surface of metatar metatarsal sal 3. This muscle is narrow at origin but broadens towards insertion before becoming tendinous. It lies posterior to extensor digitorum longus. It functions to flex the ankle joint. jo int.
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Interosseus cruris (IC) This muscle originates by a tendon at the proximo-medial tibia and fibula. It inserts via a tendon into the ventral pes. It lies between the tibia and fibula and fills the space between these two bones. It functions to assist in ankle joint flexion.
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Fig 20. Deep ventral muscles of the lower hindlimb. FB:
[email protected] NOTES Fibularis brevis, IC: Interos Interosseus seus cruris.
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The crocodilian skeleton skeleton is typical of that of tetrapods tetrapods in general and of archosaurs in particular, particular, with the skull and pelvis particularly specialised Also of interest are the structure of the head vertebrae (atlas (atlas and axis), the th e osteoderms, and the gastralia, or stomach ribs, which protect the ventral surface. As archosaurs, crocodilians are diapsid, although the post-tempora post-temporall fenestrae are reduced. Palatal Palat al and external mandibular fenes fenestrae trae and ossified la laterosphenoids terosphenoids are present. The wall of the braincase is ossified, but supratempo supratemporals rals and postfrontals postfrontals
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The pterygoid and quadrate adhere tightly to the lateral wall of the braincase and the otic notch closes clos es posteriorly. posteriorly. All species lack a parietal (pineal) foramen. The premaxillae are expanded postero-dorsally postero-dorsally,, isolating the external nares from the maxillae. Internal nares are prolonged posteriorly by a secondary palate formed of the palatal processes of the premaxillae, maxillae, palatines and pterygo pter ygoids ids and the seconda secondary ry choanae choanae open within within the ptery pterygoids goids
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Skeletal system •
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The premaxilla, maxilla and dentary bear peg-like peg -like conical thecodont teeth The largest largest teeth of the upper jaw are premaxillary premaxillary 4 in the Alligatoridae, premaxillary 5 in the Crocodylidae, and and maxillary 9 and 11 and dentary 1, 4, 11 and 12 throughout this group. The vertically undulating jawline coincides with the distribution of the largest teeth, thus accentuating the pseudoheterodonty, pseudoheterodonty, particularly in the shorter-snouted species. In the long snouted, fish-eating fi sh-eating crocodilians, the teeth are more uniform in size, approaching a homodont condition, and the jawline is
straightt rather than undulating straigh
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Skeletal system •
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The premaxilla, maxilla and dentary bear peg-like peg -like conical thecodont teeth The largest largest teeth of the upper jaw are premaxillary premaxillary 4 in the Alligatoridae, premaxillary 5 in the Crocodylidae, and and maxillary 9 and 11 and dentary 1, 4, 11 and 12 throughout this group. The vertically undulating jawline coincides with the distribution of the largest teeth, thus accentuating the pseudoheterodonty, pseudoheterodonty, particularly in the shorter-snouted species. In the long snouted, fish-eating fi sh-eating crocodilians, the teeth are more uniform in size, approaching a homodont condition, and the jawline is
straightt rather than undulating straigh
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In the Alligatoridae, the 4th dentary tooth fits into a pit in the upper jaw at the junction of premaxilla and maxilla, and the mandibular tooth rows lie inside the upper tooth rows at occlusion. In the Crocodylidae and Gavialidae, upper and lower teeth alternate at occlusion, and the 4th dentary tooth fits into a lateral not notch ch at or near the junction of the pre-maxilla with the maxilla. Thus the teeth of crocodiles are far more conspicuous than those of alligatorss when the mouth is closed. alligator
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Teeth generally are replaced continuously with new ones growing from below in the same sock socket, et, but this process slows down and stops in older individuals; some of the largestt individuals are likely larges likely to be edentulous. Cranial sculpturing becomes more complex with age as a result of secondary dermal ossifications on the dorsal surface. Some (Osteolaemus species and Palaeosuchus palpebrosus)
have palpebral osteoderms osteoderms in the upper eyelids.
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Skeletal system •
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The middle ear region is modified extensively extensively,, and the quadrate is inclined so that the hinge of the jaw is displaced far posteriorly. posteriorly. Cranial growth is allometric and the naris-eye dimension increases sever several al times faster than that between b etween eye and condyle. As the olfactory bulbs lie close to the nares, the proportions of the brain reflect those of the skull. Many cranial bones are pneumatised, and have gas-filled cavities connected to the Eustachian tubes of the middle ear and the nasal n asal passages. These may equalise pressure pressure in the inner ear , or isolate the inner ear from
underwater sounds when listening above water
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Skeletal system •
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However, pneumatisation also reduces the cranial mass (and inertia), However, while maintaining its strength, which is an important consideration in both buoyancy and feeding. The nine cervical vertebrae are keeled ventrally. The last two to five of the 15 to 16 dorsal vertebrae lack fr free ee ribs.
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The caudal vertebrae bearon relatively long two-thirds. neural and haemal spines, as well as chevron bones the anterior The cervical ribs are solid and the dorsal ones articulate ventr ventrally ally with two partly calcified elements, the ventral-most of which reaches the
sternal system.
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Skeletal system •
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The most superficial gastralia gastralia are located located between the sternal sternal region and the pelvic girdle. The shoulder girdle is simple and plate-like, and the three components of the pelvic girdle radiate from the articular fossa. The Nile crocodile has 11 to 13 thoracic ribs and six to seven abdominal ribs.
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Locomotion and buoyancy •
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Crocodilians are amphibious, but travel most easily in water which they traverse trav erse with sinuous movements of the strong, laterally compressed tail, holding the limbs at the sides. On land they have several several gaits: walking, high walking with the body held clear of the ground, running and, in some species, a galloping gait in which limbs of the two sides move in unison, driven by dorsoventr dorsoventral al flexion of the vertebral column. They also undulate down steep slopes. Galloping is a conspicuous escape movement in C. johnstoni Although they can travel at great speed, such bursts are short lived as they are sustained by anaerobic metabolism.
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Crocodiles can travel substantial substantial distances both overland and by sea
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Locomotion and buoyancy •
Crocodilians manage their buoyancy very skilfully. skilfully.
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They are denser than of water and achieve neutral buoyancy by appropriate inflation the lungs. •
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Shallowly breathing crocodilians are able to float at the water surface for long periods, the water line constant within a couple of millimetres just below the eye It is unlikely that pulmonary volume can be modified by muscular contraction contra ction during a dive, but negative ne gative buoyancy buoyancy increases with
depth as the lungs are compressed and as oxygen is removed and replaced with a smaller volume of carbon dioxide.
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Locomotion and buoyancy
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Most larger crocodilians accumulate gastroliths (stomach stones), including individuals which live in areas where stones are uncommon, implying that some effort may may be made to collect them. Larger crocodiles have a larger burden of stones
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The gastroliths do not increase specific gravity gravity,, because the crocodiles
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Crocodilians are carnivorous, sit-and-wait predators, which rely on swift attack from the water to seize s eize large terrestrial prey and immobilise it before it is swallowed. Smaller prey is commonly taken by a sideways strike strike of the head, which reduces the change of cranial momentum. It may then be broken broken up by being lifted from the water and ‘whiplashed’, in a similar manner to that used by monitor lizards. Large prey may be stored until it starts to disintegrate. In cooperative feeding, several individuals grasp a single prey item
and dismember it by twisting in opposite directions.
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Digestive syst system em •
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The hard palate and the palatal flap at the back of the buccal cavity allow food to be held in the mouth for long periods without interrupting the respiratory flow, flow, while prey is dismembered or drowned. Food is commonly picked up near the anterior tips of the jaws. It is repositioned and shifted toward the oesophagus, by inertial feeding , in which the jaws quickly release and shift the food to a new position before it can fall far.
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More effective effective in air than in water and, in addition to breathing, may explain why ingestion usually occurs with the head above the water water..
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Digestive system-oral cavity •
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The oral cavity had the form of an isosceles triangle and is dorsoventrally flattened, flattened, severely limiting the space within the cavity. cavity. The roof of the cavity is formed exclusively by the palate and the indistinct gingiva with which it is continuous. The caudal limit of the roof was demarcated by the notched dorsal component of the gular valve, whereas the rostral limit of the palate is occasionally characterised by the presence of two deep pits which accommodated the first two incisors of the mandible
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Digestive system-oral cavity •
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Between the two pits (or at the base of the two I 1 teeth) is a small, rigid, conical process which emerged e merged from a low-profiled ridge above the anterior palatine foramen. The tip of this process is housed within a shallow depression in the mandible at the base of the first two mandibular incisors. The floor of the oral cavity is formed by the tongue and a wide, rostral rostral mucosal plate continuous with the gingiva.
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Digestive system-oral cavity •
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The relatively relatively long non-protrusible tongue is roughly triangular in shape, being much broader caudally than at its tip with lingual papillae covering the dorsal surface from the root to the tip. It occupies the greater part of the floor of the oral cavity (apart fr from om the rostral plate over the symphysis symphysis of the dentary bones) and is bordered peripherally by a loose, highly folded, continuous, fibrous membrane
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Practically no function in the ingestion of food, being devoid of
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Macrophotograph aph of the mandible with the tongue in situ showing the dental arrangement arrangement Macrophotogr of the incisor (I 1 –3), canine (C 1 –5) and molar (M 1 –7) teeth, demarcated by the stippled lines. The sampling sites for histology of the gingivae (D and E) are also indicated. The rostral dentary dentary shelf is indicated in the region above the symph symphysis ysis of the dentary bones. The black arrowhead indicates the position of the shallow depression which houses the small, rigid, conically formed process,situated process,situated at the base of the I 1 teeth, seen in Fig. 2. The The glottis (GT) and laryngeal mound (LM) are shown in situ on the floor of the pharyngeal cavity and the ventral fold (VF) of the gular valve is seen separating the ventral aspects of the oral and pharyngeal cavities.
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Digestive syst system em •
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The crocodilian gut is comparatively short and simple and the viscera are typically reptilian The gastrointestinal gastrointestinal tract of crocodiles is composed of a mouth, esophagus, stomach, small intestine and large intestine without a cecum Chunks of food are swallowed whole and pass to the stomach via a long oesophagus. The stomach lies posterior to the heart, which is positioned about mid midway way between the front and rear limbs.
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The cardiac sphincter occurs occurs at the junction of the oesophagus with the cardiac sac at the left anterior corner of the stomach.
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Digestive syst system em •
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The esophagus is a straight tubular organ organ located caudally to the short pharynx, dorsally to the trachea, passing between the main bronchi of the trachea and the right and left lungs, and ending cranially in the stomach along the median line. The esophageal wall of the species examined in this study appears to be predominantly muscular, muscular, indicating a similarity to studies on Alligator Alligator mississippiensis, which apply to the other crocodilians and mammals, but differing from the latter by its greater thickness Internally, the wall shows creases arranged longitudinally, which sometimes bifurcate or converge. The middle third of the esophagus is clearly dilated and its wall is thinner
due to the passage of large food items ingested ingested by crocodilians, as reported by Santos.
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Fig. 1. Digestive system of specimens of C. crocodilus, P. palpebrosus and M. Niger from the LAPAS collection. Ventral views. A – C. crocodilus: TO, tongue; PH, pharynx; TR, trachea; ES, esophagus; RL, right lung; LL, left lung; LPB, left primary bronchus; RLL, right lobe of liver; LLL, left lobe of liver; ST, stomach; SI, small intestine; LI, large intestine; CL, cloaca. B – P. palpebrosus. PH, pharynx; ST, stomach; SP, spleen; DU, duodenum; JE, jejunum; IL, ileum; LI, large
intestine; CL, cloaca. C – M. Niger.
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Digestive syst system em •
The longitudinal creases in the proximities proximities of the gastr gastroesophageal oesophageal transition zone broaden and become less numerous, and the region becomes more constricted
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Digestive syst system em •
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The cardiac sac is divided into left and right halves by a thick collar of muscle and spongy tissue, which may operate operate as a gizzard. The pyloric region is much smaller, smaller, and opens to the duodenum via a pyloric sphincter It is likely that the cardiac (or fundic) stomach has a glandular epithelium which secretes HCl and pepsinogen,whereas pepsinogen,whereas the pyloric portion secretes secretes mucus. As crocodilians do not secrete secrete chitinases, chitinous and ker keratinous atinous remains, snail opercula and fur accumulate in crocodilian gut contents.
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Such indigestible remnants are likely to be cast out via the mouth, as in many avian species.
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system em Digestive syst •
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The main portion of the stomach is located in the left antimere in a horizontal horizont al circumvallated projection, and not immediately in the aforementioned afor ementioned antimere in an elongated and longitudinal projection, as iin n Hemidactylus mabouia. Located between the esophagus and the duodenum, it represents the most dilated part of the gastrointestinal gastrointestinal tract tract is the principal site of digestion in crocodilians and is functionally similar to the muscular stomach, or gizzard, of birds. It has a large chamber with ventral and dorsal walls of the same thickness, differing from the description given by Wallach (1971), who stated that the stomach of Caiman yacare is divided into two distinct chambers, a thick-
walled anterior one and a thin-walled posterior one, without specifying an intermediary delimitation.
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system em Digestive syst •
Four distinct gastric regions are visible: the cardia (small, and corresponding to the cranial end of the stomach, sequent to the gastroesophageal transition zone), the fundus (to the left of the gastroesophageal cardiac region, forming a conspicuous cranial angle), the corpus (the region with the largest diameter and length), and the pyloric chamber (the terminal region of the stomach, which ends in i n the pyloric
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sphincter) The cardiac region may be large or small, and that the convoluted longitudinal creases found in the stomach lumen – except in the
pyloric region due to the greater constriction constriction at its terminal end may or may not be present,
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system em Digestive syst •
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The stomach of Hemidactylus mabouia can be divided into an oral fundic, an aboral fundic and a pyloric region, while the stomach of other crocodilians is divided the into i nto a fundic and a pyloric region. In the gastroduodenal gastroduodenal transition zzone one the pyloric sphincter is visibly constricted allowing for passage to the duodenum only of liquid or pasty that has already been neutralized by mucous glands in the pyloricfood region.
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system em Digestive syst •
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Crocodilians digest flesh and bones fully fully,, including that from fresh carcasses,, and cache only very large prey for its initial dismemberment. carcasses Concerning gastrin/ cholecystekinin-lik cholecystekinin-like e hormones are secretedcontrol by the mechanisms, pyloric mucosa, and emphasise the similarity of Crocodylia to other vertebrates The stomach is situated to the left of the abdominal cavity cavity,, between the tenth thoracic and the sixth abdominal ribs, with the greater curvatur curvature e facing to the left A very acute angle is present between the cardia and pylorus An oval to round, dorso-ventrally dorso-ventrally flattened, encapsulated portion of
adipose tissue, the so-called fat body , occupies the th e right cranial part of the abdominal cavity
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system em Digestive syst •
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Starting from the pyloric sphincter sphincter,, the small intestine coils through the medial and caudal segments of the coelomic cavity cavity,, ending in the large intestine. The small intestine is divided into three segments: the duodenum, jejunum and ileum, which are continuous and devoid of a macroscopic macroscopic delimitation. These segments are identified through topographical inferences and their progressively progressive ly diminishing villosity. villosity. The duodenum begins in the right antimere lateral to the stomach. Its diameter decreases progressively progressively along its length, with a winding projection constricted at some levels, lodging the pancreas between two
well defined loops that touch the liver directly and that begin after a short transverse transver se projection,
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Fig. 2. Digestive system of a P. palpebrosus specimen from the LAPAS collection. Dorsal views. RLL, right lobe of liver; LLL, left lobe of liver; CO, direct connection of the liver to the pancreas; BDp; biliary duct emptying into the pancreas; GBl, gallbladder duct emptying into the liver; PA, pancreas; GB, gall bladder; ST, stomach; DU, duodenum; JE, jejunum; SP,, spleen. SP spl een.
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system em Digestive syst •
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The wall of the small intestine is visibly vis ibly thicker in the duodenum, presenting several several villosities in its internal anatomy anatomy,, which indicate greater adsorption capacity. These villi decrease progressively toward the caudal portion of the ileum The diameter of the large intestine is about three times larger than that of the small s mall intestine, with a dilated wall tending toward collapsibility.
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The large intestine is separated from the small intestine by a sphincter
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system em Digestive syst •
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The cloaca is located at the shared end of the digestive, urinary and genital systems. The longitudinal creases extending along its inner wall ensure considerable distension capacity
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Digestive syst system em •
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The duodenum is arranged in the form of a double loop on the right, with the pancreas situated between the arms of the th e outer loop. The pancreas also extends to the cranial broad part of the spleen and along the proximal part of the jejunum. The latter part is attached to the dorsal body wall. The ileum and jejunum, which are of equal eq ual length, fill the right and left side of the peritoneal cavity. The proximal part of the jejunum j ejunum is firmly attached to the dorsal body wall.
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The mesentery then lengthens to allow free coiling of the remaining portions of the jejunum and ileum. The rectum (in the midline) extends into the cloaca
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Digestive syst system em •
The liver, liver, which consists of right and left lobes, l obes, is situated in its own coelomic cavity, cavity, the hepatic coelom,which is bound cranially by the post-pulmonary membrane and caudally by the post-hepatic membrane.
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These two membranes are intimately associated with the cranial and
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caudal surfaces of the liver, respectively. The right and left pleural cavities communicat communicate e with the hepatic coelom by means of two openings situated left and right dorsally in
the membranous part of the post-pulmonary membrane.
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system em Digestive syst •
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The liver, liver, bilobed and with a conical shape, is located cranially in the coelomic cavity. The right lobe is larger than the left lobe, the former touching the gall bladder and the first two loops of the duodenum and the latter touching the cranial surface of the stomach. The medial dorsal and caudal region of the right lobe contains the hepatic hilum and a piriform gall bladder, bladder, which receives a hepatic duct and sends out another duct to the pancreas, as well as a
connection linked directly to the pancreas, which bifurcates bifurcates close to the hilum.
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system em Digestive syst •
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The empty gallbladder has a flattened sac-like shape and is attached caudally to the dorso-medial aspect of the right liver lobe by the hepatocystic ligament. When fully distended the gallbladder has the form of a blind-ending pouch with its body lodged ventromedially between the duodenum on the right and the stomach on the left
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system em Digestive syst •
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It should be noted that these the se ducts precede the pancreatic ducts, which in turn unite to form the hepatopancreatic ampulla, perforating the duodenum through the duodenal papilla. The biliary ducts responsible for draining draining bile from the hepatic lobes unite to form the main right and left ducts, which, together with the cystic duct, form the choledoc duct that opens into the initial portion of the duodenum. The pancreas is lodged between the first two dorsal duodenal loops, lo ops, one ascending cranially and the other descending de scending caudally, caudally, projecting
immediately after the first lateral flexure flexure to the right of the pyloric region regio n is from from the pylorus, pylorus, as in Pseudem Pseudemys ys scrip scripta ta .
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system em Digestive syst •
The pancreas extends dorsally without touching the spleen directly at its terminal segment, since the latter is attached to the medial edge of the descending duodenal flexure, differing differing from the description of Alligator mississippiensis in the direct final connection to the spleen.
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system em Digestive syst •
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The dissection of the gastro-intestinal gastro-intestinal tract revealed the stomach of which the minor curvature displayed displayed a very acute angle, resulting in the cardia and pylorus lying adjacent to each other. A pyloric antrum or dilatation is separated from the main part of the stomach by a distinct sphincter. The duodenum is arranged in a double U-shaped loop with the proximal part of the duodenum forming the inner loop and the distal part the outer loop.
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The jejunum is situated between the duodenum and ileum.
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Digestive syst system em •
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The beginning of the latter is demarcated by the presence of the A. mesenterica cranialis. An ileorectal junction is present where the narrow ileum abruptly changes into the wide rectum . The rectum continues into the cloaca
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system em Respiratory syst •
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In the Crocodilia the framework of the larynx consists of three cartilages, of which two represent the arytenoids of the Mammalia; the third represents the thyroid and cricoid of mammals. The last is considerably larger than the first and is a broad closed ring, differing in form in the different different species. The vocal apparatus is produced by the projection into the laryngeal cavity of the inner border of the small arytenoid cartilages and by the infolding, under these cartilages, of the mucous membrane of the
larynx; this forms the thick but fairly free folds that, when the glottis is narrowed, are well adapted to produce the harsh tone of the animal.
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system em Respiratory syst •
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The epiglottis is absent in the Crocodilia. At the thoracic inlet the trachea is situated to the left of the oesophagus which lies in the midline within the dorsal mesentery. mesentery. The trachea then turns abruptly to the right before dividing into a left and right primary bronchus
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In many Crocodilia the trachea forms a loop
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It is a short vertical partition in the stem just before its division into
the two branches.
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Respiratory syst system em •
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This partition is partly membranous and possesses one or more stiffening cartilaginous strands which are outgrowths of so many cartilaginous rings of the trachea. Most of the tracheal rings are closed, but a varying, though at most small, number are open on the dorsal side. These openings become wider as the larynx approach the lungs The lungs, togethe togetherr with the heart (including pericardium and the great vessels) and the oesophagus occupy the cranial half of the body cavity. The pleural cavity is divided into separate left and right cavities by means of a complete mediastinum.
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The cavities are roughly triangular in shape, with the base situated caudally and the apex terminating terminating in cupulae, both both extendin extending g a short distance (± 15 mm) beyond the first thoracic rib.
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system em Respiratory syst •
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Caudally, the pleural cavity is bound by a post-pulmonary membrane Caudally, and divided into left and right cavities by means of a complete mediastinum. The diaphragmatic surfaces of the two lungs are attached to the postpulmonary membranes, while the caudal third of the medial me dial borders are attached to the mediastinum. Each lung lies in a separate, closed pleural space, bordered laterally
by the dorsal ribs and intercostal intercostal musculature, dorsally by the vertebral column, medially by the mediastinum, and ventrally by the sternal ribs.
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system em Respiratory syst •
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The lungs, particularly in the dorsal half, half, tend to fuse with the parietal pleural surface. Right and left lungs are mirror images of each other reflected in the mediosagittal body plane. Each represents approximately approximately a truncated cone, with its base lying against the liver and its cranial apex extending ventrally into the base of the neck, between the shoulder girdle and the oesophagus. The lungs are multicameral, consisting of a variable number of chambers (camera), each of which connects independently with an unbranched, intrapulmonary bronchus
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The cranial half of the intrapulmonary bronchus is cartilage reinforced. reinforced. It displays three rows of orifices which supply four dorsal chambers, four lateral chambers and three ventral chambers
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system em Respiratory syst •
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The paired lungs are well developed and well perfused, and lie in the thorax, served by a trachea which originates anteriorly in a glottis which can be closed. The latter lies on the floor of the posterior pharyngeal cavity cavity and is supported by the cartilaginous hyoid plate. Interestingly Interes tingly,, in large C. porosus and perhaps in other species, the trachea forms a large loop in the upper thorax, reminiscent of a water-trap, but its function is unknown The Nile crocodile has 11 to 13 thoracic ribs and six to seven abdominal ribs.
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At the thoracic inlet the trachea is situated situ ated to the left of the oesophagus which lies in the midline within the dorsal mesentery. mesentery.
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system em Respiratory syst •
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The trachea then turns abruptly to the right before dividing into a left and right primary bronchus. The pleural cavity is divided into separat se parate e left and right cavities by means of a complete mediastinum. The cavities are roughly triangular in shape, with the base situated si tuated caudally and the apex terminating in cupulae, both extending a short distance beyond the first f irst thoracic rib
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system em Respiratory syst •
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Caudally, the pleural cavity is bound by a post-pulmonary membrane and Caudally, divided into left and right cavities by means of a complete mediastinum. The diaphragmatic surfaces of the two lungs are attached to the postpulmonary membranes, while the caudal third of the medial borders are attached to the mediastinum During ventilation the glottis is lifted lif ted into close proximity to the internal nares, and the gases then pass above the secondary palate to and from the exterior via the external nares. The palatal flap at the rear of the buccal cavity preven prevents ts the entry of water into the posterior pharynx, even when the open mouth holds h olds prey. prey.
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During swallowing, the glottis is closed and depressed, and the palatal flap opened.
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system em Respiratory syst •
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In crocodilians, the liver is connected to the body wall by an annulate connective tissue sheet which divides divide s the pleural and visceral cavities. Inspiration is effected by contraction of portions of the intercostal intercostal muscles which distend the rib cage, and of the m. diaphragmaticus which retracts the liver caudally. Expiration is by contraction of the superficial intercostal intercostal muscles, and of the transverse abdominal muscles which move the liver l iver forward,
thereby decreasing the pleural volume.
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Figure 40.5 Respiration in Crocodylus porosus. A, expiration; B, inspiration. lng, lungs; liv, liver; mat, m. abdominalis transversus; mdp,
[email protected] NOTES m. diaphragmaticus; mis, m. intercostalis intercostalis superficialis. [D. Kirshner]
system em Respiratory syst •
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Apart from their importance as an oxygen oxygen store and a carbon dioxide sink, crocodilian lungs are important in controlling buoyancy. Indeed, the volume of the lungs in a swimming or diving individual is determined by buoyancy requirements, not oxy oxygen gen store demands The lungs are multicameral, consisting of a variable number of chambers (camera), each of which connects independently with an unbranched, intrapulmonary bronchus .
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The cranial half of the intrapulmonary bronchus is cartilage reinforced. It displays three rows of orifices which supply four dorsal chambers, four lateral chambers and three ventral chambers.
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system em Respiratory syst •
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A medial row is lacking. The rows of orifices do not run parallel to the long axis of the intrapulmonary bronchus, but instead form a left hand spiral in the left lung (right-hand in the right lung). Hence the first lateral chamber opens into i nto the lateral aspect of the intrapulmonary bronchus, but the orifice of the fourth lateral chamber is dorsal
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The first dorsal chamber is rudimentary. rudimentary. The remaining chambers in the dorsal row are long, tubular structures.
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Respiratory syst system em •
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Together with a cluster of medial chambers which originate at the end of the cartilage-reinforced cartilage-reinforced portion of the intrapulmonary bronchus, they form a dorsomedial lung lobe. The cavernous first lateral lateral chamber extends cranially from iits ts bronchial entrance and, together with its large ventral and lateral branches, forms the lung apex Lateral Later al chambers 2-4 make up the deep lateral and superficial dorsal portions of the lung along the th e middle third of its length. In the middle third of the lung the three ventral chambers comprise comprise the
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sac like ventrolateral ventrolateral and ventromedial lung regions. The first two ventral chambers then double back dorsally and form the superficial lateral portion of the lung
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Fig. 1. Semi-schematic representation of the left lung of Crocodylus niloticus in lateral lateral view (A) and medial view (B), showing the distribution of chambers. Chambers onginating in the cartilage-reinforced cartilage-reinforced portion of the intrapulmonary bronchus (outlined by solid lines) occur in spiralling rows and are indicated: dorsal row, D1-D4; lateral row, L1-L4; ventral row, V1-V3. In the cartilage-free portion of the intrapulmonary bronchus only the major, tubular chambers are indicated by letters, indicating their dorsal (D' and D"), ventral (V and V") or lateral (L') origin. At the transition between the portions of the t he intrapulmonary bronchus a cluster of fourtwo medial chambers (M1-M4) originates. Other, smaller chambers are numerous
and irregular in occurrence. The intrapulmonary bronchus ends in a terminal chamber (T). The drawing is based upon the dissection of dried specimens from two C. niloticus and upon comparison with similar preparations from C. porosus and Caiman crocoddus. The right lung does not
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system em Respiratory syst •
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The caudal half of the intrapulmonary bronchus lacks cartilage and its chambers are not continuous with the rows described above. In additionand to the medial chambers mentioned above, fiveportions, long, tubular chambers thecluster sac-likeofterminal chamber supply the superficial while a large number of irregularly distributed outgrowths (bronchial niches) supply the deep lung parts. The inner surface of the chambers is elaborated with a system of cubicles (ediculae). The free edges of the ediculae face the central lumen of the chambers and are supported by a system of stout trabeculae, as described for amphibian and
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reptilian lungs The interedicular septa, which bear the respiratory capillaries, are often perforated, the intercameral septa, which separate adjacent chambers, rarely show whereas such perforations.
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Fig. 15. Diagrammatic images in dorsal view of (A) the pulmonary arteries and (B) pulmonary veins that are based on conventional pulmonary arteriography and CT scan 3D reconstructions. Shaded vessels in (A) are more ventrally ventrally positioned. A semitransparent semitransparent 3D airspace reconstruction stereo pair (C,D) and 3D surface volume rendering with dorsal cut away (E) are included to illustrate the challenges of interpreting the anatomy in three dimensions. Abbreviations: CVL— cranioventral lateral branch (br), CVM—cranioventral medial medi al br., br., DCrT—dorsal br. br. cranial trunk (tr.), DLcaCaT—dorsolateral caudal cauda l br. br. caudal tr., DLcrCaT—dorsolateral cranial crania l br. br. caudal cauda l tr., tr., DLCrT —dorsolateral br. cranial tr., DMcaCaT—dorsomedial caudal br br.. caudal tr tr., .,
DMcaCrT dorsomedial caudal br. br. cranial tr tr., ., DMcrCaT DMcr CaT dorsomedial cranial br b r. caudal cauda l tr., tr., DMCrT DMCr T—dorsomedial br br.. cranial tr tr., ., DMcrCrT DMc rCrT— —— dorsomedial cranial br. br. caudal cranial tr., tr., tr ., LCaT lateral br. caudalcranial tr., l tr., VMCaT—ventromedial VMCrT ventromedial crania tr., VMP—ventromedial pericardial per icardial br b r.
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Cardiovascular system •
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The crocodilian heart is most mo st sophisticated Combines features of both mammalian ,avian as well as other reptilian hearts Unlike other reptiles, crocodilians have a complete four chambered heart with two atria and two ventricles. Structure and pressure balance are similar to those of birds and mammals, with a high pressure (60 to 100 mm Hg) systemic circuit circuit
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and a low pressure (15 to 20 mm Hg) pulmonary circuit. the system also incorporates incorporates a number of unusual features which endow strong pulmonary bypass capabilities.
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Cardiovascular system •
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Firstly, the left systemic arch persists as a small vessel which leaves from the right ventricle, alongside the pulmonary p ulmonary arch! It runs dorso-laterally above the lungs to join the dorsal aorta (right systemic arch) via a small connecting vessel. However, anatomy suggests that most of its flow would be directed towards towar ds the coeliac artery rather than the th e dorsal aorta. Secondly, left and right systemic arches communicate where they cross, via a small foramen of Panizza in their common wall.
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The persistence of the left systemic arch arch and its connection from the right ventricle to the coeliac artery and the dorsal aorta affor affords ds a pulmonary bypass shunt
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Cardiovascular system •
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Normally, blood enters the left aorta from the right aorta via the foramen of Panizza, and the valves at the base of the left aorta remain closed to the right ventricle because its pressure remains lower than that in the left aorta. Hence, the left aorta normally carries well-oxygena well-oxygenated ted blood which reflects its origin from the right aorta. However, towards the end of aerobic breath-hold dives, and probably in anaerobic dives as well, the blood pressure rises in the right ventricle under the influence of pulmonary circuit vasoconstriction.
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At this stage, some low oxygen oxygen blood, otherwise destined for the lungs, is directed into the left aorta and then towards towards the gut; it does not mix with any of the oxygenated oxygenated blood until downstream of the dorsal confluence, and thus preserves a well-oxygenated supply for the head and brain.
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Cardiovascular system •
The shunt pathway may even allow a complete shutdown of the pulmonary during anaerobicdriven respiration, theright whole bodycircuit, is thenperhaps supported by perfusion by the and single ventricle.
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Experimentally blocking both pulmonary arteries achieved this result, with reversed flow through the foramen of Panizza, although whether this occurs under natural circumstances circumstances is unknown.
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Cardiovascular system •
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The heart The four-chambered heart, withthoracic a cranio-caudal orientation, is situated between the fourth and eighth ribs. The apex of the heart is attached to the pericardial sac by means of a ligament. A ligamentous attachmenmembrane. attachment t in the midline exists between the pericardial sac and the post-pulmonary
The post pulmonary membrane extends to between the ninth thoracic and first abdominal ribs. •
The dorsal partwhile of the post-pulmonary membranous, the ventral third is membrane muscular. is completely
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Cardiovascular system •
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Left and right ventricles are separate and have a complete interventricular septum. Most strikingly the left ventricle (LV) (LV) gives rise to a single aorta which whi ch supplies the body (the right aorta (RAo), whereas the right ventricle (RV), besides supplying the lungs via the pulmonary arteries (P (PAs), As), also gives rise to a major vessel supplying the body, body, the left aorta The right and left aortae cross-over one another outside the
ventricles and run down the right and left sides of the body body,, respectively
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Cardiovascular system •
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Each has a bicuspid valve at the base the right aorta being larger than the left The LAo and the RAo join twice; just outside the heart through a hole in their joint wall (the foramen of Panizza) and by a short anastomosis behind the heart The foramen of Panizza is located deep down in the valve pockets.
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Cardiovascular system •
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Aside from the heart and associated blood vessels, the blood system is essentially similar to that in other reptiles. A renal portal system is present. The extensive lymphatic system is the most complex and modified among the reptiles. It differs fromand those of other reptiles in the absence of the great sinuses and has finer more plexiform trunks which are generally similar to those of mammals.
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As the flow of lymph is driven largely by hydrostatic hydrostatic pressure, the similarity may reflect its association with a blood vascular system system which operates at higher pressures than those of most reptiles.
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Cardiovascular system •
The spleen is pear-shaped with the broad end pointing cranially and it is attached ribs to the dorsal body wall between the second and third abdominal
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Cardiovascular system •
The left (LAo) and right (RAo) aortas of crocodilians communica communicate te at two points. The inter-aortic first is the foramen of Panizza (Panizza, (Panizz a,aortic 1833),valves. an aperture in the septum just anterior to the
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The second is a vessel vesse l connecting the LAo and RAo, dorsal to the lungs, and is termed the arterial anastomosis. Posterior to the anastomosis, the LAo continues as the coeliac artery
to the gut, while the RAo becomes the dorsal aorta.
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Nervous system and sense organs •
Before Befor e dismissing the mental capabilities of crocodilians, it is as well to remember complexity of their the ir predatory and reproductive behaviour andthe their homing capacities.
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Reptilian brains are about one tenth the mass of avian or mammalian brains at comparable body size and crocodilians appear to be no exception
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Nervous system and sense organs •
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Crocodilians are well provided with sense organs, having good vision, hearing, olfaction and senses of touch. The eyes are well situated for vision in air by an almost submerged individual. While submerged, a translucent ‘third eyelid’ eyelid’,, the nictitating membrane, moves across horizontally to protect the eye. When underwater vision is probably restricted to sensing light and dark.
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Touch receptors and ears are probably the main operational sense organs underwater The eye may closed by depression of the upper eyelid, which is protected by be a bony scute.
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Nervous system and sense organs •
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Of importance in night vision is the tapetum lucidum, a layer of retinal cells which reflects incoming light, and serves as an image intensifying syst system. em. The reflective tapetum allows crocodilians to be located easily at night, the eyes reflecting the beam of a spotlight or flashlight. The iris is a vertical slit by day, day, and opens to a wide circle at night. Crocodilians vocalise when in distress and during aggressive
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behaviour, and are said to have excellent auditory capabilities. The tympanic membranes are concealed and protected by flat rectangular flaps that may be raised and lowered by muscles
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Nervous system and sense organs •
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Presumably they are closed during diving, though reception of underwater sounds is an important aspect of social communication ref to reproduction Middle ear, surrounded by bone, is more complex than in other reptiles and Olfaction originates from receptors within the nasal cavities The nasal cavities are the most complex among the reptiles and are essentially similar within the Crocodylia. Crocodylia. The nasopharyngeal ducts are elaborated elaborated dorsally in a series of sinuses, sacs and blind ducts. Adult crocodilians lack Jacobson’s organs.
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The olfactory bulbs of the forebrain are well-developed, consistent with the importance of olfaction. Taste is probably as well in the contact buds occur on theinvolved tongue and posterior palate identification of food, as taste
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Urogenital syst system em •
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The kidneys are situated caudadorsally, caudadorsally, partly within the pelvic cavity Mesonephric kidneys are the organs of ionic and osmotic regulation and of nitrogen excretion, excretion, supported by the cloaca, and lingual salt glands in the Crocodylidae but not Alligatoridae.
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All crocodilians lack a bladder.
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In fresh water, water, the cloacal urine is copious, clear and dilute, and
excess nitrogen is lost as ammonium ions, excreted as ammonium bicarbonate.
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Urogenital syst system em •
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The kidneys are situated caudadorsally, partly within the pelvic cavity The gonads lie cranio-medially to the kidneys Briefly, crocodilians have a complex social hierarchy which is established by aggression and by elabora elaborate te social signalling Large males are dominant and territorial and are thought to fertilise most of the females in a particular area. Mating occurs in the water. Females usually approach the male and an elaborate, sometimes prolonged
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courtship ensues. The individuals swim together, often in circles, make body contact frequently and rub their head over the other body (see comments on gular and paracloacal glands).
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Urogenital syst system em •
The female may flee a short distance, and draw the male into a chase
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before befor e circling is resumed. Typically females show head lifting, lifting , submissive postures.
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Copulation occurs when the male curls his tail under the female, lying to the side. In shallow water, water, both individuals indivi duals may be seen lying on their sides.
All Alligatoridae, half of the Crocodylidae and Tomistoma Tomistoma nest in mounds. •
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The remaining species use holes. Crocodylus acutus acutus nests sometimes in a hole and sometimes in a mound.
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Urogenital syst system em •
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Mound nesters lay their eggs in a nest constructed from gra grass ss or other vegetation, vegeta tion, litter, litter, and sand or soil in various proportions, depending upon what is available at the site The mound is constructed using material dug up with the hind legs, or from vegetation vegeta tion torn off with the teeth. Eggs are laid about six weeks after mating into a hole which is dug with the hind feet into the sandy substrates of a river bank.
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Though incubation time is temperature dependent, under averag average e field conditions C. johnstoni hatch after about eleven weeks. Crocodylus porosus is a mound nester and, unlike C. johnstoni, breeds in the wet season.
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system em Urogenital syst •
After courtship at the end of the dry season, nests are built at the
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onset of ‘the wet’. If the wet season begins early, early, the nesting season may be quite prolonged and tapers off towards March and April.
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Crocodylus porosus lays 50 to 60 eggs, which are heavier than those of C. johnstoni, weighing about 100 g (range 70 to 140).
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The number and size of the eggs eg gs reflects the age and size of the mother. At normal field temperatures, incubation takes about 80 to 90 days. d ays.
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Urogenital syst system em •
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The single, rigid penis is pulled out and forward by muscles. A middorsal, open groove sperm through juxtaposition with the vasa deferentia, whichreceives open dorso-laterally through the cloacal wall. The testes are paired and adjacent to the kidneys. They undergo a conspicuous annual cycle in size and activity .
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The clitoris of females is much smaller than the penis, but lies in the same position. The oviducts open o pen anteriorly to receive ova from the paired ovaries, adjacent to the kidneys.
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system em Urogenital syst •
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Each of the two oviducts opens into the cloaca via a vagina with a narrow lumen which spirals through the muscular cloacal walls How these walls relate functionally to the role of a vagina as a receptacle for for a penis, is unclear and the appropriateness of the term is uncertain.
