33-Hour Chick Reviewer

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primary brain vesicles are already present fundamental regions of the heart have already formed

Prosencephalon most anterior brain region later divides into telencephalon (anterior) and diencephalon (posterior)  both further divide into cerebral o hemispheres, thalamus, hypothalamus, and optic vesicles Prosocoel cavity of the prosencephalon  will become ventricles I to III  

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Somites 11-12 pairs are present 

 Anterior Intestinal Intestinal Portal opening of the foregut as development progresses and the gut elongates, this opening will move to the posterior  will also eventually be part of the yolk yolk stalk  

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Heart  

single, tubular, S-shaped organ at right side of the body

 Area pellucida same as 24-hour chick 

Optic Vesicle paired lateral invaginations prosencephalon opticoel - cavity of vesicle 

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Infundibulum  ventral evagination on the floor of of the diencephalon forms the posterior lobe of pituitary gland  

Mesencephalon midregion of the brain cavity: mesocoel fate of mesocoel is the aqueduct of Sylvius or o the cerebral aqueduct 

 Area vitellina vitellina same as 24-hour chick 

 Area opaca vasculosa Sinus terminalis  vein that encircles the area vasculosa vasculosa o gives rise to terminal blood vessel of vitelline o circulation 

o 

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Metencephalon anterior portion of hindbrain cavity: metacoel metacoel is part of the IV ventricle o  

Myelencephalon posterior portion of hindbrain cavity: myelocoel myelocoel is part of the IV ventricle o  

Spinal Cord neural tube posterior to the hindbrain cavity: central or spinal cord

Blood islands masses of splanchnic mesoderm o found in gut wall of amphibians and yolk sac o of amniotes form red blood cells and blood vessels o

Proamnion region that is anterior to the developing avian embryo surrounds the head contains endoderm and ectoderm  will be invaded with mesoderm and become incorporated into the amnion    

Subcephalic pocket cavity beneath the embryonic head as the head develops 

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Sinus Rhomboidalis rhomboid-shaped region located on the caudal part of the embryo this is the location of where the primitive pit and Hensen’s node are enclosed by unfused n eural folds 

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Notochord rod-like structure that is dorsal to the gut origin: mesoderm function: defines anterior/posterior axis and provides skeletal support for embryo   

Nephrotome stalk-like connection between somites and lateral plate mesoderm forms the pronephros (anterior) and mesenchyme (posterior) mesenchyme will further differentiate into o mesonephros and metanephros 

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Level of Optic Nerve Optic Vesicles lateral bulges of prosencephalon forerunners of the portions of the eyes  will ind uce the head ectoderm to thicken, t hicken, invaginate, and form the lens vesicles cavity: opticoel   

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Proamnion region below the head fold consists of ectoderm underlain with a layer of endoderm  will eventually be overgrown and disappear

Section through Oral Plate

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Prosencephalon forebrain that consists of median vesicle and a lateral outpocket on each side cavity: prosocoel 

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 Anterior neuropore neuropore median cleft at anterior tip of neural tube presence of this opening means the neural folds have not fused yet

Notochord  ventral to mesencephalon mesoderm derived  

Foregut smile-shaped cavity  ventral to notochord  walls are derived from endoderm middle portion of the foregut’s floor is slightly thickened    

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Lens Placode thickening of head ectoderm that surrounds the optic  vessel forerunner of eye lenses 

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Infundibulum shallow depression of prosencephalic floor located at posterior border of optic vessels

Oral Plate thickened area formed by the ventral ectoderm and the adjacent endodermal evagination of pharynx  ventral to the foregut  will form the mouth when it perforates 

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Subcephalic Space  below the head fold Extraembryonic Extraembryonic germ layers

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 Amniotic fold fold of somatopleure arise at the head region, the sides, and the caudal end fusion of amniotic folds will give rise to amnion (inner) and chorion (outer)

Mesencephalon oval-shaped brain vesicle posterior to prosencephalon  

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 Yolk sac extra embryonic membrane encloses and absorbs yolk of amniote embryos endoderm + splanchnic mesoderm (splanchnopleure) 

 Anterior cardinal cardinal veins paired blood vessels at the lateral sides of the mesencephalon 

Pharynx region of foregut at this level 

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Dorsal Aorta large, paired blood vessels dorsal to the pharynx 

Other structures to be noted  (description  (description in 24-hour chick) Head ectoderm Mesenchyme Neural Crest Subcephalic pocket  Area pellucida Coelom  Area Vasculosa

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Stomodeum shallow midventral depression in the ectoderm forerunner of buccal cavity  

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 Ventra Aorta Aorta small paired blood vessels located below the pharynx one is at each side of a median depression in the floor of the foregut   

First Aortic Arches connects the dorsal aorta with the ventral aorta can be seen at the anterolateral region of the foregut  

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Neural Crest cells found at the edges of the neural plate and above the neural tube  will form ganglia, pigment cells, and parts parts of the gills 

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Thyroid Gland endocrine gland that functions for control of metabolism and growth from ventral endoderm of pharynx seen as a thickened shallow depression of the foregut at the region of the dorsal mesocardium 

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Section at the level of the Heart: Posterior Sections  Atrium   

posterior level of the heart located now at the middle of the pericardial cavity  becomes the future auricles

Sinus venosus caudal continuation of the atrium dorsoventrally flattened tube in the midline  

Section at the level of the Heart: Anterior Section  Ventral Aortae Aortae fusion of ventral aorta from earlier now a median, unpaired vessel  

Bulbus arteriosus anterior chamber of heart embryo connects ventricle to the ventral aorta 

 Anterior Intestinal Intestinal Portal  ventral opening of the gut into the yolk future midgut  

 Vitelline veins paired, large vessels that enter the atrium via sinus  venosus at the caudal sections, these vessels will rise at the lateral part of the blastoderm 

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Epimyocardium outer, thicker layer of heart rudiment arises from splanchnic mesoderm fuses with the endocardium to form the heart’s wall  will give rise to: epicardium (outer covering of the heart) and myocardium (cardiac musculature) 

 Anterior cardinal cardinal veins pair of small blood vessels above the dorsal aortae also lies adjacent to the rhombencephalon  

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Isthmus  broad connection between heart and foregut synonymous to dorsal mesocardium  

rhombencephalon by the time na mag-heart na

Section at the level of the Heart: Through the  Ventricle  Ventricle  bends to one side of the coelom narrower dorsal mesocardium  

Rhombencephalon posterior part of brain level of future ventricle possesses a thick wall   

 Auditory Pits Pits ectodermal thickenings at hindbrain level forerunners to the inner ears syn: auditory placodes   

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Section through the Sinus Rhomboidalis Neural Tube neural groove has opened 

Hensen’s node  

large mass of compactly arranged cells displaces the notochordal tissue

Unsegmented mesoderm somites are not yet divided at this section Omphalomesenteric vein it is located far out in the splanchnopleure 

Section through the Somites

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Spinal Cord elongated with elliptical cavity 

Notochord Somites Nephrotome

refer to the 24-hour chick description for these structures

Hypomere Dorsal Aortae pair of large vessels between the endoderm and the somites at more caudal sections, they continue laterally into the plexus of vessels -- emphalomesenteric arteries 

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pictures are from: http://www.vcbio.science.ru.nl/images/embryology/c hicken-33hrs-dorsal-longitudinal-patten.gif http://nte-serveur.univlyon1.fr/nte/embryon/www.uoguelph.ca/zoology/devobio/33h rchck/33ckintr.htm https://embryology.med.unsw.edu.au/embryology/i mages/thumb/7/72/Patten028.jpg/600px-Patten028.jpg

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