48-Hour Chick Reviewer

48-Hour Chick Embryo: Whole Mount Changes in the 48-hour chick embryo: head fold of the amnion covers the cranial  half  half of the embryo o formation of amniotic fold o head fold + lateral amniotic fold caudal fold establishes the caudal boundary of the body o separates the embryo from underlying o  blastoderm via subcaudal pocket  beginning of this fold: concavity facing the o anterior end processes involved processes involved in the 48-hour chick: cephalization  cephalization  (rapid growth of anterior o portion)  ventral flexion (bending) flexion (bending) o at the anterior end of the embryo makes the half of formation of a pronounced cranial the embryo lie on flexure (level of midbrain) its left side  side  while the posterior half formation of an indicated cervical remains at the flexure (near hindbrain and spinal original position cord) dextral torsion (twisting) torsion (twisting) o at the anterior end of the embryo involves all of the head, both cranial and cervical flexures. heart elongation and twisting o  ventricle be comes posterior to the atrium (in o terms of location)  both these chambers are located outside of the embryo three fetal membranes that membranes  that are seen: amnion o encircles anterior portion of embryo consists of inner layer of ectoderm & outer layer of somatic mesoderm  yolk sac o double-membrane structure on left side of embryo contains blood vessels derived from endoderm and splanchnic mesoderm chorion o double-membrane structure on right side of the embryo consists of outer layer of ectoderm and inner layer of somatic mesoderm  branchial grooves and grooves and visceral  visceral arches arches  branchial grooves o  white lines that radiate out from the heart toward the auditory vesicle composed of 1st, 2nd, and 3rd  branchial grooves  visceral arches o masses of cells composed of 1st, 2nd, and 3rd  visceral arches depending on its order, each  visceral arch is located cranial to its corresponding branchial groove example: 1st visceral arch  will be cranial to the 1st  branchial groove. 1st visceral arch

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splitted into two via the stomodeum maxillary process o (anterior) mandibular o process (posterior)

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48-Hour Chick Embryo: Transverse Section

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Section through the mesencephalon Mesencephalon oval-shaped first cavity of the brain to be seen in posterior sections, the frontal section of the mesencephalon has several divisions due to cranial flexure o   

Isthmus constriction at the lengthened section of the brain partially separates the mesencephalon from the hindbrain  

Myelencephalon opposite to mesencephalon has a thin roof  

Metencephalon underlined portion of the brain  between myelencephalon and isthmus  

Mesenchyme loose connective tissues  between brain and epidermis  

Fetal Membranes refer to the whole mount descriptions 

Extraembryonic Extraembryonic Coelom space bounded by mesoderm 

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this space is between the chorion, yolk sac, and amnion

Section through the diencephalon

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ganglia of cranial nerve VII and VIII

Semilunar ganglion dark accumulation of cells at the sides of the body attached to the myelencephalon observe: root of ganglion pink structure o embedded in myelencephalon o attached to the ganglion o  

Diencephalon  when the brain separates into two cavities, it is the lower cavity replaces the mesencephalon in the preceding section 

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 Velum transversum transversum depression on the dorsal wall of the forebrain functions as a demarcation between diencephalon and telencephalon  

Metencephalon poorly defined anteriorly delimited by isthmus 

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Superior ganglion acccumulation of cells on the sides of the myelencephalon can be observed when the otic vesicle is not present anymore or it is immediately posterior to the auditory  vesicles ganglion of the glossopharyngeal (IX) nerve 

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Section through the optic cups Myelencephalon  when the brain is divided into two cavities, this is the larger and upper cavity has a thin roof  will give rise to the posterior choroid choroid plexus Semilunar ganglion dark accumulation of cells on the sides of the myelencephalon ganglion of the trigeminal (V) cranial nerve 

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Optic cup double-walled structures on the sides of the diencephalon formed via the invagination of the optic vesicles fate: sensory retina (thick, inner layer) and pigmented retina (thin, outer layer) parts of the optic cup: presumptive retina o inner layer presumptive pigmented epithelium o outer layer fate: pigmented layer of retina 

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Jugular ganglion mass of cells that is: lateral to the myelencephalon and above the anterior cardinal veins ganglion of the X cranial nerve 

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 Anterior cardinal cardinal vein space that is located on each side of the myelencephalon as the section moves posteriorly, this becomes long spaces toward the diencephalon further posteriorly, this becomes more dorsal and  becomes located ventrolateral to the myelencephalon myelencephalon 

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Lens vesicle sac-like cavity nestled within the optic cups formed via invagination of the ectoderm  

Optic stalk connects optic cup with the diencephalon 

Pharynx cavity below the notochord triangular in shape middle portion = pharynx proper o arms of triangle = 1st pharyngeal pouch (or o hyomandibular pouch) 1st pharyngeal pouch  will invaginate to form the 1st branchial o groove the double layered membrane formed by the o invagination is called the 1st closing plate or 1st branchial plate 

Notochord  vacuolated cells between the myelencephalon and the diencephalon tracing posterior, splits into two due to cranial flexure in succeeding structures, will eventually unite back into one, single structure 

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Section through the otic vesicle Otic vesicle paired vesicle on each side of the myelencephalon formed as an invagination of the ectoderm in older specimens, an invagination at the dorsal wall of the otic vesicle is the forerunner forerunner of of the endolymphatic duct   

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Preoral gut anterior most part of the foregut small circle or oval structure which is separated from the pharynx via the oral plate fingerlike diverticulum anterior to the future mouth  

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 Anterior cardinal cardinal vein pair of blood vessels located on ventro-lateral to the otic vesicles  

Carotid loop extensions of the 1st aortic arches medial to the anterior cardinal veins  

 Acoustico-facialis ganglion dark accumulation of cells close to are sometimes attached to the otic vesicle and anterior cardinal vein located lateral to the myelencephalon 

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Internal carotid arteries paired vessels extensions of the carotid loops  

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alongside forebrain medial to the optic cups

Dorsal aorta  blood vessels on the sides of the notochord notochord above the above the 1st pharyngeal pouch  

First aortic arch  blood vessels below the below the 1st pharygneal pouch  becomes located within the mandibular process process eventually becomes continuous with the ventral aorta   

 Visceral arches  between two pharyngeal pouches lateral walls of the visceral arches: thickened o filled with mesenchymal cells o 

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even more posteriorly, posteriorly, ventral ends of the 2nd aortic aortic arch become continuous with the ventral aorta

2nd pharyngeal pouch outpocketing of the pharynx can be seen when the otic vesicle is not seen or at the posterior sections of the otic vesicle  

 Ventral aorta aorta  blood vessels located beneath the pharynx the following vessels are continuous with this:  bases of the first aortic arch arch o  ventral ends of the 2nd aortic arch o  ventral ends of the 3rd aortic arches arches o  

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Mandibular arch more anterior of the rounded mesenchymal masses masses  between it lies the stomodeum gives rise to the jaws  bears the first aortic arch arch syn: 1st visceral arch

aortic arches

 ventral aorta

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Maxillary arch rounded or flattened masses on the sides of the Rathke’s pouch  

Rathke’s pouch small vesicle located between the infundibulum and the pharynx arises as a dorsal evagination of t he stomodeum fate is the hypohysis    

Oral plate thin line made of ectoderm and endoderm separates the stomodeum and pharynx syn: pharyngeal membrane   

Infundibulum arises as an evagination from the diencephalon extends in the direction of the foregut later evaginate to become the posterior (neural) lobe of pharynx  

Section through the third aortic arch 3rd pharyngeal pouch outpocketing of the pharynx pharynx + 3rd pharyngeal pouch = laterally oriented oral cavity  

3rd aortic arch  beneath the 3rd pharyngeal pouch not well developed another pair of downward extensions from t he dorsal aorta  ventral ends are continuous with the ventral aorta   

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3rd visceral arch  between 2nd and 3rd pharyngeal pouch arches that are posterior to the hyoid arch are sometimes referred to as branchial as branchial arches this is because in lower vertebrates these o arches will bear the gills  

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Diencephalon more elongated at this level 

Stomodeum slit-like slit-like space where the Rathke’s pouch opens 

Notochord as previously described 

Section through the thyroid rudiment and the second aortic arch Thyroid rudiment depression on the floor of the pharynx 

2nd aortic arch  blood vessels beneath the 2nd pharyngeal pouch located within the 2nd visceral arch (hyoid arch) posteriorly, extend downward from the dorsal aorta  

Bulbus cordis first heart cavity to be observed differentiated from the ventral aorta due to the presence of both an endocardium and endocardium and a myocardium  

Dorsal mesocardium mesodermal stalk attaches the stalk to the dorsal wall of the coelom  

Nasal placode thickened skin ectoderm lateral to the telencephalon  

1st somite compact cell masses composed of: dermatome o darkly stained cells  beneath skin ectoderm future dermis of the skin  

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myotome lightly stained cells medial to future dermatome future muscle  

Lung buds evagination on the ventro-lateral portions of the foregut into the pleural cavity 

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 Anterior cardinal cardinal veins  becomes more ventral separates into two vessels: postcardinal vein (dorsal) and common cardinal vein (ventral)  

Section through the atrium and ventricle Spinal cord replaces the myelencephalon at this level 

Descending aorta fused dorsal aortae 

Dorsal intersegmented arteries small blood vessels arising at intervals from the d orsal aorta extends dorsally between spinal cord and somite  

Pleural cavity portion of coelom that is lateral to the developing lung  buds it is continuous with the pericardial cavity 

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Transverse septum mesenchyme surrounding the sinus venosus from where the dorsal mesocardium connects the heart to the dorsal body wall connected with the pleuropericardial membrane  

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Cranial liver diverticulum small mass of cells dorsal to the sinus venosus lies in the transverse septum (ventral to foregut) a diverticulum from the wall of the gut gives rise to the liver syn: dorsal diverticulum   

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Conus arteriosus chamber of the heart at the right side of side of the embryo endocardium and myocardium are widely separated  

 Atrium  

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at the left side of side of the embryo endocardium and myocardium are in close contact  with each other future auricles

Caudal liver rudiment  branch or branches on ventral side of cranial liver rudiment syn: ventral diverticulum 

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Duodenum  when the cranial liver rudiment becomes continuous  with the foregut 

Section through the anterior intestinal portal

 Ventricle large looped chamber of the heart connects the conus arteriosus and the atrium

 Anterior intestinal intestinal portal opening of foregut to the midgut floor of midgut is the yolk

Laryngotracheal groove  V-shaped depression in the floor of the foregut foregut develops into: larynx, trachea, and lung buds

 Vitelline veins pair of blood vessels extensions of the sinus venosus located on each side of the anterior intestinal portal the left vitelline vein passes out onto the yolk  first   before the right vitelline vein

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Future esophagus dorsal portion of the gut  will later differentiate from part of the foregut (which is dorsal to the laryngotracheal groove) 

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Peritoneal cavity space where internal organs are located 

Cardinal Veins paired precardinal veins (or anterior cardinal veins) separates into two: postcardinal vein - dorsal o common cardinal vein - ventral o 

Section through the sinus venosus Sinus venosus portion of the heart that is attached to the foregut via the dorsal mesocardium

Paired mesonephric duct small tubules lateral to descending aorta mesonephric tubule rudiments medial to the mesonephric duct o  will undergo cavitation to cavitation to form mesonephric o tubules of the paired mesonephric kidneys formed via delamination of the nephrogenic cord (nephrotome)  

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Common cardinal vein  blood vessel to which the sinus venosus venosus is attached 

Pleuropericardial membrane mesenchyme that encloses the common cardinal vein separate pleural cavity from the pericardial region of the coelom 

Section through the lateral amniotic folds Lateral amniotic folds elevated folds that are about to fuse continuous with the lateral body walls consists of somatopleure forms inner amnion and outer chorion o   

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 Vitelline blood blood vessels small blood vessels within the splanchnic mesoderm 

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Paired dorsal aortae large pair of blood vessels below the notochord descending aorta has not formed at more caudal levels  

Mesonephric tubule rudiments round cavity medial to the mesonephric duct 

Nephrostome opening of mesonephric tubule to the coelom 

 Vitelline arteries arteries extension of dorsal aorta onto the yolk sac 

Section through the tail bud Tail bud mass of mesenchymal cells at caudal end of the embryo covered by skin ectoderm 

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note: the tail bud is a mesoderm derived structure but it is covered by ectoderm

Hindgut posterior portion of the gut now has a floor  

 Allantoic rudiment endoderm lined cavity located below the tail bud 

Caudal intestinal portal space where the floor of the allantoic rudiment disappears opening of hindgut into the yolk 

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