24 hour Chick
WHOLE MOUNT 1. Area Opaca
- 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
3. Primitive streak
- 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 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 6. Neural groove
- Median longitudinal groove
- Formed by rolling up the neural plate 7. Head fold
- Folded region of the blastoderm
- Dark crescent line marking the boundary of the head of the embryo 8. Notochord
- Longitudinal band of cells extending causal from the region of the neural folds to the Hensen’s node
9. Foregut
- First part of the digestive tract
- Floor is composed of endodermal cells - Dome shaped inside the head
10. 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 11. Mesenchyme of the head
- Lose network of cells in the space between the foregut and at the ectoderm of the head
12. 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
13. Somites
- From the division of the dorsal mesoderm - 3 – 4 pairs lateral to the plate mesoderm 14. 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
- Margins of the neural epithelium - Fused at the midline
3. Anterior neuropore
- Temporary external opening of the neurocoel 4. Neural groove
- Median longitudinal groove
- Formed by rolling up the neural plate 5. Prechordal plate
- Mass of chordamesodermal cells - Anterior to the notochord
- Forms the HEAD MESENCHYME 6. Notochord
- Small medial mass between the foregut and the neural plate 7. Foregut
- Dorsoventral flattened tube with endodermal cells - Beneath the neural plate
8. Oral plate
- Where floor of the foregut is in contact with the neural ectoderm of the head - BREAKS OPEN TO BECOME THE MOUTH
- Synonym: oropharyngeal membrane 9. Mesenchyme
- Loosely scattered cells
- Fills up the space between the foregut and the neural plate 10. Proamnion
- Region of the blastoderm beneath the head - Ectoderm and endoderm only
11. Subcephalic pocket
- Cavity formed beneath the head as the head folds develop 12. Somatopleure
- Membrane composed of ectoderm and somatic mesoderm - Forms PART OF THE BODY WALL, CHORION, AND AMNION 13. Splanchnopleure
- Cellular layer splanchnic mesoderm and endoderm
- Forms PART OF THE BODY WALL, YOLK SAC, AND ALLANTOIS 15. Coelom
- Cavity when the somatic mesoderm and the mesoderm separates 16. Subgerminal cavity
- Space beneath the hypoblast within the AP - Rise to a MIDGUT
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 1. Neural tube
- Tube of tissue by thickening and rolling up the neural plate during neurulation - Forms the BRAIN AND SPINAL CORD
2. Neural Crest
- Edges of the neural plate above the neural tube
- Migrate to form GANGLIA, PIGMENT CELLS, PARTS OF THE GILL ARCHES, ETC. 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
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 1. Somites
- Segmented mesodermal blocks on the side of the spinal cord - Rose from dorsal mesoderm
2. Nephrotome
- Stalk-like connection between somites and lateral plate mesoderm - Anteriorly = PRONEPHROS
- Posteriorly = mesenchyme = MESONEPHROS and METANEPHROS - Synonym: intermediate mesoderm, mesomere, nephromere 3. Hypomere
- Mesoderm distal to the nephrotome - SOMATIC AND SPLANCHNIC MESODERM
Section through the Primitive Streak
- Consists of primitive groove and 2 primitive ridges 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
- Synonym: forebrain 2. Optic Vesicle
- Paired lateral evaginations on the sides of the prosencephalon - Contains opticoel
3. Infundibulum
- Ventral evagination of the floor of the diencephalon - Forms the POSTERIOR LOBE OF THE PITUITARY GLAND 4. Prosocoel
- Cavity of the prosencephalon - Rise to VENTRICLES 1 TO 3
THOC
Intermediate mesoderm
Lateral plate mesoderm Dorsal mesoderm
5. Mesencephalon
- Mid region of the brain - Cavity is mesocoel
- Forerunner of the aqueduct of sylviu/ cerebral aqueduct
- Synonym: midbrain 6. Rhombencephalon
- 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
- Region of the neural tube posterior to the myelencephalon - Narrow cavity: central/ spinal cord
8. Sinus rhomboidalis
- Rhomboid shaped region at the caudal region
- Primitive pit and hensen’s node are enclosed by unfused neural folds 9. Notochord
- Rod like structure originating from the mesoderm and dorsal to the gut - Defines the anterior/posterior axis
- For skeletal support 10. Nephrotome
- Stalk like connection between somites and lateral plate mesoderm - Anteriorly = PRONEPHROS
- Posteriorly = mesenchyme = MESONEPHROS and METANEPHROS - Synonyms: intermediate mesoderm, mesomere, nephromere 11. Somites
- 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
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
- Forebrain
- Consists of median vesicle and lateral out pocketing per side 2. Anterior neuropore
- Median cleft at the anterior tip of the neural tube - Indicates that neural folds have not yet fused 3. Prosocoel
a. Optic vesicle
– Paired lateral evaginations on the sides of the prosencephalon
– Contains opticoel b. Opticoels
4. Lens placode
- Thickening of the head ectoderm overlying the optic vessel - Forerunner of the eye lens
5. Infundibulum
- Shallow depression of the prosencephalic floor of at the posterior border of the optic vessels
6. Amniotic fluid
- 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 7. Yolk Sac
- Extra embryonic membrane enclosing and absorbing the yolk in amniotes - From a layer of endoderm and layer of splanchnic mesoderm
(splanchnopleure) 8. Head ectoderm
- Cuboidal cells enclosing the head 9. Mesenchyme
- Fills up the space between the foregut and the neural plate 10. Neural crest
- Migrate to form GANGLIA, PIGMENT CELLS, PARTS OF THE GILL ARCHES, ETC. 11. Subcephalic Pocket
- Cavity formed benath the head as the head folds develop 12. 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
13. Coelom
- Cavity when the somatic mesoderm and the mesoderm separates 14. Area vasculosa
- Inner region
- Thickening of splanchnic mesoderm - Forms BLOOD ISLANDS
15. Proamnion
- Anterior to the developing avian embryo, surrounding the head - Only endoderm and ectoderm
- Will become INVADED WITH MESODERM AND INCORPORATED INTO THE AMNION
16. Foregut
- First part of the digestive tract
- Floor is composed of endodermal cells - Dome shapped inside the head
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 2. Bulbus arteriosus
- Anterior chamber of the heart which connects the ventricle to the ventral aorta
- Synonym: bulbos cordis, conus arteriosus, truncus arterioisus 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)
4. Isthmus
- Broad connection between the heart and the foregut - Synonym: dorsal mesocardium
Section through the future ventricle 1. Ventricle
- Region of the heart that bends to one side of the coelom - Dorsal mesocardium is narrower
2. Rhombencephalon
- Posterior part of the brain at the level of the future ventricle - Thick wall
3. Auditory pits
- Paired ectodermal thickenings at the hindbrain - Forerunners of the inner ear
- Synonym: auditory placodes 4. Neural crest
- 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 2. Notochord
- Longitudinal band of cells extending causal from the region of the neural folds to the hensen’s node
3. Somites
- Segmented mesodermal blocks on the side of the spinal cord - Rose from dorsal mesoderm
4. Nephrotome
- Stalk-like connection between somites and lateral plate mesoderm - Anteriorly = PRONEPHROS
- Posteriorly = mesenchyme = MESONEPHROS and METANEPHROS - Synonym: intermediate mesoderm, mesomere, nephromere 5. Hypomere
- Mesoderm distal to the nephrotome - Somatic and splanchnic mesoderm 6. Dorasal aortae
- Pair of large vessels between the endoderm and somites
- Continue laterally into the plexus of vessels = EMPHALOMESENTERIC ARTERIES 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
