24 33 Hour Chick

24 hour Chick WHOLE MOUNT 1. Area Opaca -

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Peripheral region surrounding area pellucida and in contact with the yolk (dark color & nutrition) 3 zones a. Peripheral region – Margin of growth – Cells proliferate but no contact with the yolk b. Zone junction – Intermediate region where cells cut free from the yolk and are added to the area pellucida c. Inner zone – Germ wall – Originates from zone junction and have yolk granules – Transition region for the area pellucida 2 regions a. Vasculosa – Inner region – Thickening of splanchnic mesoderm – Forms BLOOD ISLANDS b. Vitellina – Outer region – No blood islands

2. Area Pellucida -

Central region of blastodisc Forms PRIMITIVE STREAK Lies over the subgerminal cavity and is translucent because of the thinness of the blastoderm a. Epiblast: outer = ectoderm and mesoderm b. Hypoblast: inner

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Longitudinal cleft formed on the surface of the amniotic blastodisc by convergence of cells Gastrulation begins as the epiblast cells migrate towards and into the streak a. Primitive groove – Central furrow thickening b. Primitive ridges – Margins of the primitive streak flanking the primitive groove on either side c. Primitive pit – Indented region of the blastoderm at the anterior end of the primitive streak d. Henson’s node (Viktor Hensen, German anatomist and physiologist) – Thickened area at the anterior end of the primitive streak through which cells invaginate to form the NOTOCHORD. – Homologous to the dorsal lip of the blastopore in amphibian embryos – Synonym: primitive knot

3. Primitive streak -

4. Proamnion -

Anterior to the developing avian embryo, surrounding the head Only endoderm and ectoderm Will become INVADED WITH MESODERM AND INCORPORATED INTO THE AMNION

5. Neural folds -

Margins of the neural plate that will fuse at the mid dorsal region

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Median longitudinal groove Formed by rolling up the neural plate

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Folded region of the blastoderm Dark crescent line marking the boundary of the head of the embryo

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Longitudinal band of cells extending causal from the region of the neural folds to the Hensen’s node

6. Neural groove

7. Head fold

8. Notochord

9. Foregut

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13. 14.

- First part of the digestive tract - Floor is composed of endodermal cells - Dome shaped inside the head Anterior intestinal portal (AIP) - Opening of the foregut in amniotes - Prominent arched line beneath the neural folds - Continuous with the lateral walls of the foregut - OPENING MOVES POSTERIORLY AND ULTIMATELY BECOMES PART OF THE YOLK Mesenchyme of the head - Lose network of cells in the space between the foregut and at the ectoderm of the head Mesoderm a. Anterior border of the mesoderm – Faint line across the A.P. – Anterior end of the notochord b. Thickened splanchnic mesoderm – Darker line of the lateral border of the AIP – Formed by delamination of the lateral plate mesoderm – Forms the HEART Somites - From the division of the dorsal mesoderm - 3 – 4 pairs lateral to the plate mesoderm Unsegmented mesoderm - Undivided region of the mesoderm posterior to the somites Transverse section

1. Head ectoderm -

Cuboidal cells enclosing the head Cuboidal origin

2. Neural folds

3. 4.

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Anterior neuropore Neural groove Prechordal plate Notochord

Margins of the neural epithelium Fused at the midline Temporary external opening of the neurocoel Median longitudinal groove Formed by rolling up the neural plate Mass of chordamesodermal cells Anterior to the notochord Forms the HEAD MESENCHYME

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Small medial mass between the foregut and the neural plate

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Dorsoventral flattened tube with endodermal cells Beneath the neural plate

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Where floor of the foregut is in contact with the neural ectoderm of the head BREAKS OPEN TO BECOME THE MOUTH Synonym: oropharyngeal membrane

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Loosely scattered cells Fills up the space between the foregut and the neural plate

7. Foregut

8. Oral plate

9. Mesenchyme

10. Proamnion

11. 12.

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15. 16.

Subcephalic pocket Somatopleure Splanchnopleure Coelom Subgerminal cavity -

Region of the blastoderm beneath the head Ectoderm and endoderm only Cavity formed beneath the head as the head folds develop Membrane composed of ectoderm and somatic mesoderm Forms PART OF THE BODY WALL, CHORION, AND AMNION Cellular layer splanchnic mesoderm and endoderm Forms PART OF THE BODY WALL, YOLK SAC, AND ALLANTOIS Cavity when the somatic mesoderm and the mesoderm separates Space beneath the hypoblast within the AP Rise to a MIDGUT

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Section through the Anterior Intestinal Portal Neural folds already formed the neural tube Open foregut and its endoderm is continuous with the rest of the endoderm Opening of the closed foregut= AIP Thickened splanchnic mesoderm = PROSPECTIVE CARDIAC MESODERM

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Tube of tissue by thickening and rolling up the neural plate during neurulation Forms the BRAIN AND SPINAL CORD

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Edges of the neural plate above the neural tube Migrate to form GANGLIA, PIGMENT CELLS, PARTS OF THE GILL ARCHES, ETC.

1. Neural tube

2. Neural Crest

3. Head fold - Downward bend of the membranes around the head region 4. Anterior Intestinal Portal (AIP) - Opening of the foregut in developing amniotes - Gut elongates and moves posteriorly to BECOME PART OF THE YOLK SAC 5. Amnio-Cardiac Vesicle - Region of the coelom - Give rise to the HEART AND AMNION - Thickened splanchnic mesoderm makes the proximal wall of the semi-cardiac vesicle = forerunner of the heart - Dorsal wall of the vesicle, somatopleure, = AMNION - Middle part contains the yolk = MIDGUT - Embryo was removed from the yolk for fixation, yolk at the bottom 6. Midgut - Floorless region posterior to the AIP

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Section through the Somite Neural folds are not closed Developed from the dorsal mesoderm Lateral and adjacent to it = intermediate mesoderm = KIDNEYS Lateral plate mesoderm = SOMATIC AND SPLANCHNIC MESODERM

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Segmented mesodermal blocks on the side of the spinal cord Rose from dorsal mesoderm

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Stalk-like connection between somites and lateral plate mesoderm Anteriorly = PRONEPHROS Posteriorly = mesenchyme = MESONEPHROS and METANEPHROS Synonym: intermediate mesoderm, mesomere, nephromere

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Mesoderm distal to the nephrotome SOMATIC AND SPLANCHNIC MESODERM

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Section through the Primitive Streak Consists of primitive groove and 2 primitive ridges

1. Somites Dorsal mesoderm

2. Nephrotome Intermediate mesoderm

3. Hypomere Lateral plate mesoderm

1. Primitive streak -

Longitudinal cleft on the surface of the amniote blastodisc by convergence of cells Gastrulation: epiblast migrate into the streak a. Hensen’s node – Anterior end of the primitive streak – Cells invaginate = NOTOCHORD – Homologous to the dorsal lip of a blastopore in amphibians – Synonym: primitive knot b. Primitive pit – Depression, slightly deeper than the groove and posterior to hensen’s node c. Primitive groove – Posterior cut reveals the central furrow d. Primitive ridges – Thickened margins on the side of the primitive groove

33 hour chick Whole mount 1. Prosencephalon -

Most anterior brain region DIVIDES INTO TELENCEPHALON AND DIENCEPHALON Differentiate into CEREBRAL HEMISPHERES, THALAMUS AND HYPOTHALAMUS, AND OPTIC VESICLES THOC Synonym: forebrain

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Paired lateral evaginations on the sides of the prosencephalon Contains opticoel

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Ventral evagination of the floor of the diencephalon Forms the POSTERIOR LOBE OF THE PITUITARY GLAND

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Cavity of the prosencephalon Rise to VENTRICLES 1 TO 3

2. Optic Vesicle

3. Infundibulum

4. Prosocoel

5. Mesencephalon 6. Rhombencephalon -

Mid region of the brain Cavity is mesocoel Forerunner of the aqueduct of sylviu/ cerebral aqueduct Synonym: midbrain Most posterior region of the brain Synonym: hindbrain a. Metencephalon – More anterior – Cavity: metacoel – Part of the 4th ventricle b. Meyelencephalon – More posterior – Last part of the brain – Cavity: myelocoel – Part of the 4th ventricle

7. Spinal cord

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Sinus rhomboidalis Notochord Nephrotome Somites -

Region of the neural tube posterior to the myelencephalon Narrow cavity: central/ spinal cord Rhomboid shaped region at the caudal region Primitive pit and hensen’s node are enclosed by unfused neural folds Rod like structure originating from the mesoderm and dorsal to the gut Defines the anterior/posterior axis For skeletal support Stalk like connection between somites and lateral plate mesoderm Anteriorly = PRONEPHROS Posteriorly = mesenchyme = MESONEPHROS and METANEPHROS Synonyms: intermediate mesoderm, mesomere, nephromere 11 – 12 pairs

12. Anterior Intestinal Portal (AIP) - Opening of the foregut - Gut elongates and moves posteriorly to BECOME PART OF THE YOLK SAC 13. Foregut - Faint lines from the margins of AIP 14. Heart - Single, tubular, S-shaped organ bulging to the right side of the body 15. Area Pellucida and Area Vitellina - Central region of blastodisc - Forms PRIMITIVE STREAK - Lies over the subgerminal cavity and is translucent because of the thinness of the blastoderm a. Epiblast: outer = ectoderm and mesoderm b. Hypoblast: inner - Outer region and no blood islands (av) 17. Area opaca vasculosa a. Sinus terminalis – Vein encircling the area vasculosa – ARISE TO THE TERMINAL BLOOD VESSEL OF THE VITELLINE CIRCULATION

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b. Blood islands – Masses of splanchnic mesoderm – Form FIRST RED BLOOD CELLS AND BLOOD VESSELS – Found in the guts of wall of amphibians and yolk sac in amniotes c. Proamnion – Anterior region surrounding the head in avians – Only ectoderm and endoderm – Become INVADED WITH MESODERM AND INCORPORATED IN AMNION d. Subcephalic pocket – Cavity formed beneath the embryonic head as head fold develops TRANSVERSE SECTION Section at the level of the Optic Nerve Optic vesicles as lateral bulges of prosencephalon Optic vesicles are forerunners of the retina Overlies the head ectoderm Induce ectoderm to thicken = LENS VESICLES Proamnion consists of an ectodermal layer which will eventually be gone Lack of mesoderm makes it stain pale in whole mounts

1. Prosencephalon 2. Anterior neuropore 3. Prosocoel

Forebrain Consists of median vesicle and lateral out pocketing per side Median cleft at the anterior tip of the neural tube Indicates that neural folds have not yet fused a. Optic vesicle – Paired lateral evaginations prosencephalon – Contains opticoel b. Opticoels

on

the

sides

of

the

4. Lens placode -

Thickening of the head ectoderm overlying the optic vessel Forerunner of the eye lens

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Shallow depression of the prosencephalic floor of at the posterior border of the optic vessels

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Fold of somatopleure arising first at the the head, the at the sides, then at the caudal end Fusion of the amniotic folds = INNER AMNION AND OUTER CHORION

5. Infundibulum

6. Amniotic fluid

7. Yolk Sac -

Extra embryonic membrane enclosing and absorbing the yolk in amniotes From a layer of endoderm and layer of splanchnic mesoderm (splanchnopleure)

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Cuboidal cells enclosing the head

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Fills up the space between the foregut and the neural plate

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Edges of the neural plate above the neural tube

8. Head ectoderm 9. Mesenchyme 10. Neural crest

11. Subcephalic Pocket 12. Area pellucida -

Migrate to form GANGLIA, PIGMENT CELLS, PARTS OF THE GILL ARCHES, ETC. Cavity formed benath the head as the head folds develop Central region of blastodisc Forms PRIMITIVE STREAK Lies over the subgerminal cavity and is translucent because of the thinness of the blastoderm a. Epiblast: outer = ectoderm and mesoderm b. Hypoblast: inner

13. Coelom -

Cavity when the somatic mesoderm and the mesoderm separates

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Inner region Thickening of splanchnic mesoderm Forms BLOOD ISLANDS

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Anterior to the developing avian embryo, surrounding the head Only endoderm and ectoderm Will become INVADED WITH MESODERM AND INCORPORATED INTO THE AMNION

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First part of the digestive tract Floor is composed of endodermal cells Dome shapped inside the head

14. Area vasculosa

15. Proamnion

16. Foregut

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Scetion through the oral plate Notochord ventral to the midbrain/mesencephalon Foregut, vental to the notochord, smile-shaped cavity with thin endoderm walls Mid portion of the foregut is slightly thickened Below the foregut is the ectoderm, oral plate = MOUTH Below the head is the subcephalic space and extra embryonic germ layers

1. Mesencephalon - Oval brain vesicle posterior to the prosencephalon 2. Anterior cardinal veins - Paired blood vessels lying at the lateral sides of the mesencephalon 3. Pharynx - Region of the foregut 4. Dorsal aorta - Large, paired blood vessels dorsal to the pharynx 5. Stomadeum - Shallow midventral depression in the ectoderm - Forerunner of the buccal cavity 6. Oral plate - Thickened area formed by the ventral ectoderm of the head and the adjacent endodermal evagination of the pharynx 7. Ventral aorta - Small paired blood vessels lying below the pharynx, one on each side of a median depression in the floor of a foregut 8. First aortic arches - Blood vessels that connect the dorsal aorta with the ventral aorta - Anterior sections at the anterolateral region of the foregut

Section at the level of the Heart Anterior Sections 1. Ventral Aortae -

Median unpaired vessel formed by the fusion of the paired ventral aortae

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Anterior chamber of the heart which connects the ventricle to the ventral aorta Synonym: bulbos cordis, conus arteriosus, truncus arterioisus

2. Bulbus arteriosus

3. Epimyocardium -

Outer thick layer if the heart Rose from the splanchnic mesoderm Fuses with endocardium = HEART Gives RISE TO THE EPICARDIUM (outer covering of the heart) and MYOCARDIUM (cardiac musculature)

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Broad connection between the heart and the foregut Synonym: dorsal mesocardium

4. Isthmus

Section through the future ventricle 1. Ventricle 2. Rhombencephalon 3. Auditory pits 4. Neural crest -

Region of the heart that bends to one side of the coelom Dorsal mesocardium is narrower Posterior part of the brain at the level of the future ventricle Thick wall Paired ectodermal thickenings at the hindbrain Forerunners of the inner ear Synonym: auditory placodes Group of cells found at the edges of the neural plate, abve the neural tube Migrate to form the GANGLIA, PIGMENT CELLS, PARTS OF THE GILL ARCHES, ETC.

5. Thyroid Gland -

Endocrine gland in the throat region, above the neural tube Controls the metabolism and growth From a ventral diverticulum of the endoderm of the pharynx Thickened shallow depression of the foregut at the dorsal mesocardium Posterior sections

1. Atrium -

Posterior level of the heart when it goes back to the middle part of the pericardial cavity Forerunner of the future auricles

2. Sinus venosus - Caudal continuation of the atrium - Dorsoventral flattened tube in the midline 3. Anterior intestinal portal - Margin of the ventral opening of the gut into the yolk - Floorless gut becomes the MIDGUT -

4. Vitelline veins - Paired large vessels that enter the atrium via sinus venosus - Arise laterally onto the blastoderm 5. Anterior cardinal veins - Pair of small blood vessels above the dorsal aortae and adjacent to the rhombencephalon Sections through the somites 1. Spinal cord -

Neural tube is elongated Elliptical cavity Cns region

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Longitudinal band of cells extending causal from the region of the neural folds to the hensen’s node

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Segmented mesodermal blocks on the side of the spinal cord Rose from dorsal mesoderm

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Stalk-like connection between somites and lateral plate mesoderm Anteriorly = PRONEPHROS Posteriorly = mesenchyme = MESONEPHROS and METANEPHROS Synonym: intermediate mesoderm, mesomere, nephromere

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Mesoderm distal to the nephrotome Somatic and splanchnic mesoderm

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Pair of large vessels between the endoderm and somites Continue laterally into the plexus of vessels = EMPHALOMESENTERIC ARTERIES

2. Notochord

3. Somites

4. Nephrotome

5. Hypomere

6. Dorasal aortae

Section through the Sinus Rhomboidalis 1. Neural Tube -

Neural groove is open

2. Hensen’s Node - Large mass of compact cells displacing the notochord tissue 3. Unsegmented Mesoderm - Somites are not yet divided 4. Primitive Streak - Posterior section, neural groove has flattened and disappeared - Remains of the primitive streak 5. Omphalomesenteric Vein - Far out in the splanchnopleure