48-HOUR CHICK EMBRYO WHOLE MOUNT -
body is thicker and more opaque cranial half of embryo covered with head fold of the amnion this fold moves posteriorly over the embryo, meets the lateral amniotic body fold from the sides and together forms that amniotic fold the caudal part does not show such covering; instead, start of the tail or caudal fold starts to establish the caudal boundary of the body such that the embryo is separated from the underlying blastoderm by the subcaudal pocket (The beginning of this fold is to be seen as a concavity facing the anterior end.) along with the rapid growth of the anterior portion (cephalization) of the chick embryo, it also shows both ventralflexion (bending) and dextral torsion (twisting) of the anterior end = half of the total length of embryo lies in its left side while the posterior half remains in original position cranial flexure at the midbrain level is quite pronounced, while cervical flexure (near junction of hindbrain and spinal cord) is just indicated Torsion involves all of the head, both cranial and cervical flexures Heart has elongated, twisted upon itself Ventricle later comes to lie posterior to the position of the atrium; both chambers lie outside the body of the embryo
3 fetal membranes are observable here: 1. Amnion – encircles the anterior portion of the embryo and consists of an inner layer of ectoderm and an outer layer of somatic mesoderm 2. Yolk sac – double-membraned structure lying on the left side of the embryo and contains blood vessels; derived from endoderm and splanchnic mesoderm 3. Chorion – double-layered membrane which lies on the right side of the embryo; consists of an outer layer of ectoderm and an inner somatic mesoderm, lying close to the amnion -
3 irregular white lines can be seen radiating out from the heart toward the auditory vesicle: Most anterior 1st branchial groove, 2nd branchial groove, and the last is 3rd branchial groove 1st visceral arch: mass of cells cranial to the 1st branchial groove; partially splitted into 2 processes by another line, the stomodeum 2nd visceral arch: between the 1st and 2nd groove 3rd visceral arch: between the 2nd and 3rd groove Maxillary process of the 1st visceral arch: process anterior to the stomodeum Mandibular process of the 1st visceral arch: process posterior to the stomodeum
STRUCTURE Mesencephalon
LOCATION Oval shaped and the 1st cavity of brain to be observed
Isthmus
Constriction at the lengthened
TRANSVERSE SECTION SECTION THROUGH THE MESENCEPHALON FUNCTION HOW IS IT FORMED?
Partially separates the
ORIGIN
FATE -moving posteriorly, section lengthens, showing a frontal section of the several divisions of the brain (due to cranial flexure)
section of the brain Myelencephalon Metencephalon Mesenchyme Fetal membranes Extraembryonic coelom
Thin roof of the brain found at the opposite end of the mesencephalon Underlined portion of the brain section between the myelencephalon and isthmus Loose connective tissues between the brain and the epidermis Space between the chorion, yolk sac, and amnion
Diencephalon
Velum transversum
Depression found in the dorsal wall of the forebrain
Metencephalon
Still poorly defined and anteriorly delimited by isthmus Upper, larger cavity of the 2 brain cavities which has a thin roof Dark accumulation of cell on each side of the body closer to the myelencephalon Masses of cells found lateral to the myelencephalon and above the anterior cardinal veins Space lined by very thin wall along each side of the
Myelencephalon Semilunar ganglion Jugular ganglion Anterior cardinal vein Syn: Precardinal vein
mesencephalon from the hindbrain
*refer to the descriptions given in the previous section* Bounded by mesoderm SECTION THROUGH THE DIENCEPHALON Replaces the position Lower cavity when the occupied by the brain separates into 2 mesencephalon in the cavities as the section is preceding position traced posteriorly Serves as the demarcation between the diencephalon and telencephalon In later dev’t, will form the posterior choroid plexus Ganglion of the trigeminal (V) cranial nerve Ganglion of the X cranial nerve When the section is moved posteriorly, It
myelencephalon
Notochord
Small, elongated mass of vacuolated cells that appear between the myelencephalon and the diencephalons
Otic Vesicle Syn: Auditory vesicle, Otocyst
Paired vesicle on each side of the myelencephalon
Anterior cardinal vein
Pair of blood vessels on the ventro-lateral side of the otic vesicle Dark accumulation of cells close to (and sometimes attached to) the otic vesicle and anterior cardinal vein, and lateral to myelencephalon Dark accumulation of cell on each side of the body attached to the myelencephalon *Observe the root of ganglion (pink structure seemingly embedded in the myelencephalon and attached to the ganglion)
Acoustico-facialis ganglion
Semilunar ganglion
breaks into long spaces toward the diencephalons. Further posteriorly, lies progressively more dorsal and soon lie on both ventrolateral side of the myelencephalon Tracing posteriorly, it separates immediately into 2 (due to cranial flexure), eventually becomes one in the succeeding section SECTION THROUGH THE OTIC VESICLE Starts to be formed as an invagination of the ectoderm
Ganglia of VII and VIII cranial nerves
Ganglion of the trigeminal (V) cranial nerve
In the dorsal wall of the vesicle of older specimens, a small invagination, the forerunner of endolymphatic duct, can be observed
Superior ganglion
Accumulation of cells on both sides of the myelencephalon which is observed eother when the otic vesicle is no longer present or immediately posterior to the auditory vesicles
Optic cup
Double-walled structures on each side of the diencephalons
a. b.
SECTION THROUGH THE OPTIC CUPS Sensory retina (thicker Derived from the optic layer) vesicles by invagination Pigmented retina (thinner layer)
Presumptive retina Presumptive pigmented epithelium
Lens vesicle
Inner layer of the cup Outer layer of the cup, later become the pigmented layer of the retina Little sac-like cavity nestled within the optic cups
Optic stalk Pharynx
a.
Ganglion of the glossopharyngeal (IX) nerve
1st pharyngeal pouch (hyomandibular pouch)
1st closing plate/ 1st branchial plate Preoral gut
Arises as an invagination of the ectoderm Connects the optic cup with the diencephalon
Cavity, which started as a hole below the notochord is now triangular Middle portion of the pharynx proper and the arms of the triangle
Projects from the pharynx proper dorso-laterally and then invaginates to form the 1st branchial groove Double-layered membrane formed
Anteriormost part of the foregut seen as small circle or oval
structure separated from the pharynx by oral plate
Carotid loop Internal carotid arteries
Dorsal aorta 1st aortic arch
Extends forward as a fingerlike diverticulum anterior to the future mouth Elongated spaces medial to the anterior cardinal veins Paired vessels extending from the carotid loops alongside the forebrain and medial to the optic cups Blood vessels on either side of the notochord and lies aboce the 1st pharyngeal pouch Blood vessels that lie beneath the 1st pharyngeal pouches
Extensions of the 1st aortic arches
Tracing posteriorly, it becomes located within the mandibular processes Further posteriorly, paired aortic arches approach one another and becomes continuous with ventral aorta
Visceral arches
Mandibular arch Syn: 1st visceral arch Maxillary arch
Found between two pharyngeal pouches These lateral walls are greatly thickened and filled with mesenchymal cells The more anterior of the 2 rounded mesenchymal masses between which lies the stomodeum The other rounded or flattened masses on either side of the Rathke’s pouch
Bears the 1st aortic arch
Named as such because they will form the jaws
Rathke’s pouch Oral plate Syn: Pharyngeal membrane Infundibulum
Diencephalon Stomodeum Notochord Thyroid rudiment 2nd aortic arch
Small vesicle between the infundibulum and pharynx Thin line
Ventral aorta Syn: Aortic sac
Separating the stomodeum and pharynx
Later form the hypophysis Ectoderm and endoderm
Evagination from the diencephalons extending in the direction of the foregut More elongated in shape in this section Slit-like space where Rathke’s pouch open As previously described SECTION THROUGH THE THYROID RUDIMENT AND 2ND AORTIC ARCH Depression in the floor of the pharynx Blood vessels that lie beneath the 2nd pharyngeal pouches Contained within the 2nd visceral arches (hyoid arches)
2nd pharyngeal pouch
Dorsal evagination of the stomodeum
2nd outpocketing of the pharynx, seen at the posterior sections of the otic vesicle or when the otic vesicle is not seen anymore Blood vessels beneath the pharynx Starts where the bases of the 1st aortic arches meet Ventral ends of 2nd aortic
Later evaginate the posterior (neural) lobe of the hypophysis
Posteriorly, these blood vessels extend downward from each dorsal aortae Ventral ends become continuous with the ventral aorta a few sections more posteriorly
Further traced posteriorly, appearance of 2 layers in its wall indicates the beginning of bulbus cordis
arches become continuous with this sac also, likewise the ventral ends of the dev’ing 3rd aortic arches SECTION THROUGH THE 3RD AORTIC ARCH RD
3 pharyngeal pouches
3rd aortic arches
3rd visceral arch
Bulbus cordis
Dorsal mesocardium Nasal placode
Large outpocketing of the pharynx Together with the pharynx gives a laterally oriented oval cavity Located beneath the 3d pharyngeal pouch (not welldeveloped yet) Another pair of downward extensions from the dorsal aorta Located between the 2nd and 3rd pouches Arches posterior to the hyoid arch are sometimes referred to as branchial arches because in the lower verts, they bear the gills 1st heart cavity to be observed in the series Presence of endocardium and myocardium differentiate it from the ventral aorta of the preceding section Mesodermal stalk that attaches the heart to the dorsal wall of the coelom Thickened skin ectoderm
Ventral ends of these vessels as mentioned before is also continuous with the ventral aorta
1st somite Each somite is composed of: a. Dermatome b.
Myotome
Anterior cardinal veins
Spinal cord Descending aorta Dorsal intersegmented arteries Conus arteriosus
Atrium
lateral to the telencephalon Compact cell masses lying immediately lateral to the myelencephalon Plate of darkly stained cells beneath the skin of ectoderm
Dermis of skin
Plate of lightly stained cells medial to the future dermatome Located progressively ventrally
Muscle Separates into 2 vessels at the level lateral to foregut:
Postcardinal vein (dorsal) Common cardinal vein (ventral) SECTION THROUGH THE ATRIUM AND VENTRICLE Section of the CNS present in this section Fused dorsal aorta Small blood vessels arising at intervals from dorsal aorta and extending dorsally between spinal cord and somite Heart chamber at the right side of embryo Endocardium and myocardium widely separated Heart chamber at the left side of embryo Endocardium and myocardium are in close contact with each other
Replaces myelencephalon in the series
Auricles
Ventricle Laryngotracheal groove Future esophagus
Large looped heart chamber Deep V-shaped depression in the floor of foregut; seen in more posterior sections Dorsal portion of gut
Cardinal veins
Paired precardinal veins progressively located ventrally
Sinus venosus
Portion of the heart attached to the foregut by means of the dorsal mesocardium Blood vessel to which the sinus venosus is attached Mesenchyme enclosing the common cardinal vein
Common cardinal vein Syn: Duct of Cuvier Pleuropericardial membranes Lung buds
Pleural cavity
Transverse septum
Connects conus arteriosus and atrium Later develops larynx, trachea, and the lung buds Later differentiate from the part of the foregut dorsal to the laryngotracheal groove Separates into 2 vessels at a level lateral to the foregut: Postcardinal vein (dorsal) Common cardinal vein (ventral) SECTION THROUGH THE SINUS VENOSUS
Separates the pleural cavities from the pericardial region of the coelom Slight evagination on the ventro-lateral portions of the foregut into the pleural cavities
Paired portions of the coelom lateral to the developing lung buds and continuous with the pericardial cavity Mesenchyme surrounding the
sinus venosus from where the dorsal mesocardium connects the heart to the dorsal body wall, in this case, the level of the foregut
Cranial liver diverticulum Syn: Dorsal diverticulum
Caudal liver rudiment Syn: Ventral diverticulum *Trace the connections of the two liver diverticula to the gut Duodenum
Anterior intestinal portal
Vitelline veins Syn: Omphalomesenteric vein *Trace them and note that first the left, then the right
Connected with the pleuropericardial membrane Small mass of cells on the dorsal side of the sinus venosus lying in the transverse septum ventral to the foregut
Liver arises as a diverticulum from the wall of the gut
Branch/es on the ventral side of the cranial liver rudiment appearing in more caudal sections. If the series is moved posteriorly, the cranial liver rudiment becomes continuous with the foregut SECTION THROUGH THE ANTERIOR INTESTINAL PORTAL Opening of foregut to the midgut The floor of midgut is the yolk so that after the removal of the yolk in the slide prep, a space is left which represents the midgut Pair of blood vessels which are the posterior extensions of the sinus venosus These are also the same blood
vitelline veins pass out into the yolk Peritoneal cavity Paired mesonephric duct
Lateral amniotic folds
Vitelline blood vessels Paired dorsal aortae
Mesonephric tubule rudiments
vessels that lie on each side of the anterior intestinal portal Big space where the organs are Small tubules lateral to the descending aorta
Medial to this are the mesonephric tubule rudiments which will undergo cavitation to form mesonephric tubules of the paired mesonephric kidneys SECTION THROUGH THE LATERAL AMNIOTIC FOLDS Elevated and about to fuse Consists of folds somatopleure that forms inner amnion Continuous with the lateral and outer chorion body walls Small blood vessels embedded within the splanchnic mesoderm Big pair of blood vessels below the notochord *Note that the descending aorta has not yet formed at more caudal levels Round cavity medial to the mesonephric duct which is the first observed at this level
Nephrostome Vitelline arteries
Formed by delamination from the nephrogenic cord (nephrotome)
Opening of the mesonephric tubule to the coelom *Trace the dorsal aorta until it extends onto the yolk sac as the vitelline arteries
SECTION THROUGH THE TAIL BUD Tail bud Hindgut Allantoic rudiment Caudal intestinal portal
Mass of mesenchymal cells at the caudal end of the embryo and covered by skin ectoderm Posterior portion of gut where it acquires a floor Endoderm-lined cavity below the tail bud Space where the floor of the allantoic rudiment disappears
Opening of the hindgut in the yolk
72-HOUR CHICK EMBRYO WHOLE MOUNT 1.
Note the changes in shape In addition to the cranial/cephalic flexure in 48-hr chick embryo, two other flexures have appeared: Cervical/Nuchal flexure at the level of the first several somites
2. o o o o o o o o o o o o o o o o
Tail flexure at the caudal end of the embryo Amnion and Chorion enclosed the entire embryo Paired wings and lung buds are visible but not sharply bounded Allantois, a sac-like structure, is somewhat encircled by the tail Take note of the ff. structures: Telencephalon Nasal pits Diencephalon Pineal gland Optic cups Optic fissure Lens vesicle Infundibulum Rathke’s pouch Mesencephalon Metencephalon Isthmus Myelencephalon Auditory vesicle Endolymphatic ducts Spinal cord TRANSVERSE SECTION
Trace the ff. structures in an ANTEROPOSTERIOR SEQUENCE Identify the 3 fetal membranes STRUCTURE LOCATION Metencephalon Anterior part of the hindbrain, has thicker walls than myelencephalon Boundary between metencephalon and myelencephalon is indistinct Roof of this structure undergoes enlargement ->
FUNCTION
HOW IS IT FORMED?
ORIGIN
FATE
Myelencephalon
Neuromeres
Posterior choroid plexus Endolymphatic ducts
Auditory vesicles Syn: otic vesicle, otocysts
Acoustico-facialis ganglia
Cerebellum of brain Posterior part of the hindbrain Lying freely within the cavity of this structure is the thin roof plate of the myelencephalon Segmented enlargements in the walls of the myelencephalon and metencephalon Thin roof of the myelencephalon which is folded in the myelocoel Structures appeared alongside the walls of the myelencephalon
Gives rise to the future roof of meulla and adjacent skin ectoderm Brain of chick embryo composed of 11 neuromeres: Forebrain: 1st, 2nd, 3rd Midbrain: 4th and 5th Hindbrain: 6th-11th Where vascularization occurs
Small, thick-walled oval structure that appears before the auditory vesicle comes into view Bigger than the endolymphatic duct *The level at which auditory vesicles appeared first, 2 groups of nerve fibers arise from neuromeres cranial to each auditory vesicle and become continuous with the ganglia on each side Dark mass of cells lying against the cranial wall of
As you trace a few section more posteriorly, the preceding structure become continuous with the auditory vesicles which are located at the level of the 10th neuromere one on each side of the myelencephalon. Ganglia of the VII (facial) and VIII (auditory) nerves
the auditory vesicles Spinal cord a. Central canal b. Roof plate c. Floor plate d. Sulcus limitans
Central cavity of SC Thin mid-dorsal wall of SC Mid-ventral wall of SC Lateral depression of the central canal about midway between the floor and roof plates
e.
Alar plates
Dorso-lateral wings of SC Wall between sulcus limitans and roof plate
f.
Basal plates
Ventro-lateral wings of SC Wall between sulcus limitans and floor plate
Membranes of spinal cord: a.
b.
Marginal layer
Oute region of neural tube composed of several fibers and fewer nuclei
Ependymal layer
Single, innermost layer of cells adjacent to central canal; cells here are capable of mitosis
c. Mantle layer Semilunar ganglion Syn: Gasserian ganglion
Wide, heavily, nucleated layer between marginal and ependymal layers Very large, dark mass anterior to acoustico-facialis ganglion
Each one of these ganglion subdivide into 3 branches which are actually branches of the trigeminal nerve: a.
Maxillary branch b. Opthalmic branch c. Mandibular branch Superior ganglion *Trace its nerves (glossopharyngeal nerves) into the 3rd branchial arch Somite *Trace this caudally and identify the dermatome, myotome, and sclerotome Mesencephalon
These 3 branches are located within the region of the 1st branchial arch, which fade out caudally Medial branch Lateral branch closest to mesencephalon Lateral branch above the ophthalmic branch Poorly circumscribed Very small, rounded accumulation of cells located on the caudal side of each auditory vesicle Compact cell masses lying immediately lateral to the myelencephalon Small, rounded region lying beneath the metencephalon with its cavity
Mesocoel -> Cerebral aqueduct/ Aqueduct of Sylvius In a more posterior section, this mesencephalon becomes continuous with the metencephalon
Oculomotor nerve (III) *Trace the mesencephalon posteriorly Anterior cardinal vein Syn: Precardinal vein *Trace caudally and note
Collectively, nerve fibers from the neural ectodermal cells appeared as pair of streaks from the floor of mesencephalon. Large vein, represented by space, is found laterally situated in the mesenchyme
Will innervate 4 pairs of extrinsic eye muscles
change in position Notochord
Closing plates
of the floor of the myelencephalon Elongated mass of cells found between 2 regions of the hindbrain or between the spinal coed and the hindbrain Double-layered membranes
Pharyngeal furrowa
1st pharyngeal furrow and pouch
2nd pharyngeal furrow and pouch In more posterior sections, trace 3rd and 4th pharyngeal furrows and pouches, and closing plates Visceral arches
Mandibular arch
Pouch: appears as an isolated structure which soon become continuous with the pharynx and open outside via the 1st pharyngeal furrow Similar in appearance with the 1st one Only more posterior (towards SC) At this level, 1st and 2nd pouches fade out Found between adjacent pharyngeal furrows These lateral walls are greatly thickened and filled with mesenchymal cells Mass of mesenchyme
FOREGUT AND ASSOCIATED STRUCTURES Formed by endoderm of pharyngeal pouches and ectoderm of pharyngeal furrows Invagination of pharyngeal pouches projected lateral from the pharynx to contact the adjacent region of the skin ectoderm Pouch: endodermal evagination Furrow: V-shaped ectodermal indentation
Maxillary arch
Hyoid arch
Symphysis of the lower jaw Dorsal aorta
1st aortic arch 2nd, 3rd, 4th aortic arches
Ventral aorta Syn: aortic sac, truncus arteriosus
Descending aorta
anterior to the 1st furrow (towards mesencephalon) Lobe-like mass of mesenchyme anterior to the stomodeum Found in the same mass of mesenchyme where the mesencephalon is found Mesenchyme found between 1st (hyomandibular) pouch and furrow and the 2nd furrow *Trace the mandibular arch posteriorly and note the 2 arches fuse ventrally Paired structures which are cut frontally on each side of the foregut Appear constricted into 2 parts at the level of 1st pharyngeal pouch Lies within the mandibular process Extend from the dorsal aortae into the 2nd, 3rd, and 4th branchial arches respectively At section of 1st aortic arch, seen as separate vessels in the mandibular arch. Caudally, they approach one another and becomes continuous Seen posterior to the 3rd
In posterior sections, ventral ends of the 2nd and 3rd aortic arch also unite in the ventral aorta Result from fusion of
Internal carotid artery *Trace it forward around the Rathke’s pouch and along the sides of infundibulum
Jugular ganglion
pharyngeal pouch Narrower vessel observed to be located in the mesenchyme lateral to notochord
paired aorta Cranial extension of dorsal aorta
Located medial to the anterior cardinal vein and is seemingly broken into 2 segments by the pharyngeal pouch Dark, smaller mass of cells lying posterior to the IX nerve
Derived from the group of neural crest cells
Thyroid rudiments
Oral plate Syn: pharyngeal membrane Preoral gut
Stomodeum
Rathke’s pouch
Thin membrane
Small gut pocket, which is located just cranial to the oral plate, which becomes less conspicuous after the rupture of oral plate Slit-like space, lined by ectoderm and lies between 2 visceral masses next to the foregut An irregular cavity lined with cuboidal epithelium that opens in more posterior sections into the
Separates stomodeum from foregut, which ruptuers to form the mouth opening
Serves as rudiment of the anterior pituitary gland
Arises from the floor of pharynx as a median diverticula/depression at the level between the 1st and 2nd pair of pharyngeal pouches Apposition of pharyngeal endoderm and stomodeal ectoderm
Ganglion fades our within the 4th branchial arch
Laryngotracheal groove
Trachea
stomodeum V-shaped ventralmost part of the posterior section of foregut Seen at level of 4th pharyngeal pouch when foregut starts to elongate ventrally In some sections, lies beneath the esophagus region
Lung buds
Pleural cavities
Esophagus
Mediastinum
Coelomic cavities lateral to the lung buds and continuous with the pericardial cavities Dorsal rounded part of the foregut, now separated from the laryngotracheal groove as a result of its constriction Both the esophagus and lung buds are contained within a thick mesentery composed of splanchnic mesoderm Whole mesenchymal mass where the esophagus and lung buds are embedded Includes the dorsal
Arises with the lung buds as ventrocaudal diverticulum of pharynx Paired bilateral expansion of the laryngotracheal groove
Posterolaterally, each lung bud is cut off from the laryngotracheal groove so that the doughnut-like structure appears (future bronchi -> lung bud proper)
Bulbus cordis Syn: conus arteriosus, bulbus arteriosus
Atrium
Sinus venosus *Trace caudally and note that it becomes continuous with common cardinal vein Ventricle
Trabeculae
mesentery (spec. mesoesophagus in this section) and ventral mesentery (dorsal mesocardium) *As the aortic sac is traced caudally, note the appearance of the endocardium and myocardium, which will indicate the beginning of the bulbus cordis Large chamber lying to the left of and caudally to the bulbus cordis Usually has blood corpuscles in it Appearing on the dorsal part of atrium, this chamber is attached to the foregut by dorsal mesocardium and is separated from the atrium by a slight constriction Trace the heart region posteriorly until left and right regions of heart are fused No clear delineation among the chambers but the ventricle can be identified by means of thick wall Irregular projections of myocardium especially numerous in the ventricular walls
Pericardial cavity Common cardinal vein Syn: duct of Cuvier
Pleuropericardial membrane Syn: Lateral mesocardium Transverse septum
Part of coelom immediately surrounding rhe heart Blood vessels found continuous to and on each side of sinus venosus
Bridge of mesenchyme through which common cardinal vein passes Mass of mesenchyme
Trace it anteriorly and observe the 2 blood vessels that are located within the right lateral body wall that separates the heart Common cardinal vein (lower vessel) Posterior cardinal vein (upper vessel) Separates in a limited region the pleural and pericardial cavities Icompletely separating the pericardial cavity from peritoneal cavity Encloses the veins that enter the heart
Peritoneal cavity
Diencephalon Infundibulum Optic cup Retina
Body cavity posterior to the transverse septum which is continuous with both the pleural and pericardial cavity Laterally compressed and has thinner walls Appeared in sections posterior to the oculomotor nerves Not connected to the diencephalon in the first sections encountered Inner layer of optic cup differentiate into: a. Sensory retina:
Replaces mesencephalon Long ventral outpocketing of diencephalon Formed by invagination of the optic vesicles
Optic fissure Syn: Choroid fissure Lens vesicle
Corneal epithelium
Optic stalk
Postcardinal vein
thick layer next to lens vesicle b. Pigmented retina: thin external layer Seen as a ventral gap in the optic cup
Formed by the ventral invagination of optic cups and optic stalks
Lens has become freed from the superficial skin ectoderm which will later form the corneal epithelium Now it forms a completely closed vesicle and begins to differentiate into 2 regions: a. Elongates and centrally located cells that will form the lens fibers b. Outer, narrower layer of cells that will become the lens epithelium Single layer of epithelial tissue Aggregations of mesenchymal cells outside the optic cup Continue to trace the section posteriorly, optic cups become continuous with diencephalons via optic stalk Blood vessel, in a more caudal section, become located progressively more
Covers the lens of eye Sclera and choroids coat of eyes
Intersegmental vein
Stomach
Dorsal mesogaster Hepatogastric ligament Syn: ventral mesogaster Ductus venosus
Anterior liver diverticula Syn: Cranial liver diverticula Mesoduodenum Hepatoduodenal ligament Syn: Duodenohepatic ligament Posterior liver diverticulum Syn: Caudal liver diverticulum
dorsally and eventually lies dorsal to mesonephros Small blood vessels that appear as extensions of the postcardinal vein Trace esopahagus posteriorly until the diameter of the gut becomes larger; lies medial to pleural cavities Mesentery dorsal to stomach Mesentery ventral to stomach Large vessel that has become of the sinus venosus posteriorly Surrounded by a thick wall of mesenchyme and embedded in it are the liver diverticula Seen at about the level of stomach lying just above the ductus venosus Mesentery lying dorsal to the duodenum Mesentery lying ventral to the duodenum Lie beneath the ductus venosus and connecting duodenum
Drain blood from the dorsl organs like somites, notochord, neural tube, etc.
Pronephros *Look for nephrostomes (openin of pronephros to the coelom) Allantoic vein Syn: umbilical vein *Size difference between the L and R
Small tubes found ventrolateral to the dorsal aorta Found on lateral body wall
Drains blood from the allantois
Proceed caudally until the section is cut through both the diencephalon and telencephalon Appears in more posterior The cavity of the section with its lateral, ovaltelencephalon has 3 shaped evagination called divisions: telencephalic vesicles, a. Median which will become the telocoel/ future cerebral Ventricle III: hemispheres, lying on connects either side of the median posteriorly with portion of the said division the diocoele b. Two lateral Dorsally, the diencephalon diocoele/ is still present overhanging Ventricles I the telencephalon and II: connect with the medial telocoel through the foramen of Monro Lamina terminalis Thin section of the anterior telencephalic wall Nasal placodes Thickened layer from the Syn: Olfactory placode skin ectoderm lateral to the telencephalon Nasal pit Ectodermal invagination Openings to outside -> Syn: Olfactory pit on each side of External nares telencephalon As you continue posteriorly, note the disappearance of the diencephalon and telencephalon; now trace the SC throughout its length at the opposite end of the section studied Vitelline veins 2 big blood vessels at this Telencephalon
Syn: Omphalomesenteric veins
level of the gut on each side of the cranial liver diverticulum
The liver diverticula arise as two buds on the duodenum of birds as compared to amphibians which arise as ventral evagination of the foregut Cranial intestinal portal Encountered when Syn: Anterior intestinal specimen is traced more portal posteriorly at the level of duodenum to a position ventral to ductus venosus Wing buds Caudal to the cranial Composed of a core of intestinal portal, wing buds somatic mesoderm appear as conical bulges on covered by the skin each side of the body ectoderm which is thickened laterally as the apical ectodermal ridge Intersegmented arteries Small blood vessels continuous with the dorsal aorta UROGENITAL SYSTEM Mesonephric duct Tiny duct with thick wall on Formed by cavitation of Syn: Wolffian duct each side at about the level the mesonephric duct of wing buds rudiments
Mesonephric tubules Mesonephric ridge
Subcardinal veins
Situated far laterally and ventral to the posterior cardinal vein Paired S- shaped tubules medial to each mesonephric duct Rounded bulge of the dorsal body wall into the peritoneal cavity containing the mesonephros Small blood vessels lying beneath each mesonephric
Mesonephric kidneys
Leg buds Tail bud Allantois *Trace posteriorly and note conncetion between hindgut and allantois Chorio-allantoic membrane
kidney Lie at level of posterior intestinal portal Large mass of undifferentiated cells Dark mass with irregular sacculation located to the right of the hindgut in the extraembryonic coelom Lies immediately beneath the inner shell membrane
Yolk sac
Chorion
Outer wall of each amniotic fold
Amnion
Inner wall of each amniotic fold
Extraembryonic coelom Syn: Exocoel Hindgut Lateral body fold
Remnants of the primitive streak and knot Store nitrogenous waste product and serves as embryonic respiratory organs for birds For respiration and absorption of calcium for the shell Endodermal cells of yolk sac digest the yolk which are transported to the dev’ing embryo via vitelline veins
Formed from splanchnopleure
Formed from the splanchnopleure that overgrows the yolk Consists of ectoderm on the outside with an adjacent layer of mesoderm inside to form the chorion Consist of somatic mesoderm on the outside ad ectoderm on the inside to form the amnion
Somatic mesoderm-lined cavity within each amniotic fold which is continuous with th intraembryonic coelom Endoderm-lined cavity; posterior region of gut Together with the head and tail folds to which it connects, forms the boundary between the
embryonic and extraembryonic regions Cloaca
Cloacal membrane Syn: Anal plate Caudal intestinal portal Syn: Posterior intestinal portal
Posterior portion of hindgut which continuous ventrally with the allantois and mesonephric ducts In more posterior sections Double-layered membrane where the ventralendoderm of the cloaca fuses with ventral skin ectoderm Tracing the section anteriorly, note the disappearance of the floor of hindgut Thus, an opening is formed from the hindgut into the subgerminal cavity via caudal intestinal portal
Upon rupture, it will establish the anal opening
