Transverse Section 1) Metencephalon – anterior part of hindbrain - thicker walls than myelencephalon - indistinct boundary between meten and myelencephalon - fate of its roof: cerebellum 2) Myelencephalon – posterior part of hindbrain - fate of its thin roof (Posterior Choroid Plexus): roof of medulla (& adjacent ectoderm) 3) Neuromeres – segmented enlargements - found on walls of meten & myelencephalon - 11 neuromeres: > Forebrain – 1st to 3rd > Midbrain – 4th to 5th > Hindbrain – 6th to 11th 4) Posterior Choroid Plexus – thin roof of myelencephalon - folded in the myelocoel - vascularization occurs here 5) Endolymphatic Ducts – @ sides of myelencephalon walls - small, thick-walled oval structure - appears before auditory vesicle does 6) Auditory Vesicles / Otic Vesicles / Otocysts - @ level of 10th neuromere - on each side of myelencephalon - bigger than endolymphatic duct *Going posterior, on each side: 2 groups of nerve fibers, continuous to ganglia
7) Acoustico-facialis Ganglia (AFG) – dark cell masses - lie against cranial wall of otic vesicle - Facial (VII) + Auditory (VIII) ganglia 8) Spinal Cord a. Central Canal – central cavity b. Roof Plate – thin mid-dorsal wall c. Floor Plate – mid-ventral wall d. Sulcus Limitans – lateral depression of central canal - midway between floor and roof plates e. Alar Plates – dorsoventral wings - wall between sulcus limitans and roof plate f. Basal Plates – ventrolateral wings - wall between sulcus limitans and floor plate g. Membranes 1. Marginal Layer – outer; several fibers, fewer nuclei 2. Ependymal Layer – single, innermost; adjacent to central canal; mitotic cells 3. Mantle Layer – wide; heavily nucleated; between marginal and ependymal 9) Semilunar Ganglion / Gasserian Ganglion – very large, dark mass - anterior to AFG - subdivide into 3 (branches of Trigeminal Nerve): 1. Maxillary branch – medial 2. Ophthalmic branch – lateral branch closest to mesencephalon 3. Mandibular branch – lateral branch above ophthalmic arch 10) Superior Ganglion - very small, rounded cell accumulation - @ caudal of sides of otic vesicles - nerves: Glossopharyngeal Nerves - can be traced into 3rd branchial arch 11) Somite – compact cell masses - immediately lateral to myelencephalon - w/ dermatome, myotome, sclerotome 12) Mesencephalon – small, rounded region beneath metencephalon - cavity: Mesocoel (future Cerebral Aqueduct / Aqueduct of Sylvius) - posteriorly becomes continuous w/ metencephalon
13) Oculomotor Nerve (III) – group of nerve fibers that appear as a pair of streaks from the mesencephalic floor - innervate 4 pairs of extrinsic eye muscles 14) Anterior Cardinal Vein (ACV) / Precardinal Vein – found in mesenchyme of mesencephalic floor - large vein; represented by space 15) Notochord – elongated cells - between 2 regions of hindbrain / between spinal cord and hindbrain FOREGUT & Associated Structures: 1) Closing Plates – double layered membranes - endoderm (of pharyngeal pouches) + ectoderm (pharyngeal pouches) 2) Pharyngeal Furrows – from invagination of pharyngeal pouches 3) 1st Pharyngeal Furrow and Pouch (PF & P) – endodermal evagination - (in this section) isolated structure, becomes continuous w/ pharynx - opens externally via 1st Pharyngeal Furrow - (furrow) V-shaped ectodermal indentation 4) 2nd PF & P – similar in appearance than 1st - more posterior (towards spinal cord)
3rd and 4th PF & P and closing plates – more posterior; @ w/c 1 st and 2nd fade out
5) Visceral Arches – between adjacent PFs - thickened and filled w/ mesenchymal cells 6) Mandibular Arch – mass of mesenchyme - anterior to 1st PF (towards mesencephalon) 7) Maxillary Arch – lobe-like mass of mesenchyme - anterior to stomodeum - found in same mass of mesenchyme where mesencephalon is found 8) Hyoid Arch – mesenchyme between 1st (hyomandibular) pouch & furrow and 2nd furrow 9) Symphysis of Lower Jaw – where 2 arches of mandibular arch fuse ventrally (posterior) 10) Dorsal Aorta – paired - cut frontally @ sides of foregut - constricted into 2 parts @ level of 1st pharyngeal pouch
11) 1st Aortic Arch – w/in mandibular process 12) 2nd-4th Aortic Arches – from dorsal aortae into 2nd-4th branchial arches respectively 13) Ventral Aorta / Aortic Sac / Truncus arteriosus – separate vessels of 1st aortic arch (@ mandibular arch level) unite - (posterior) ventral ends of 2nd and 3rd aortic arch unite 14) Descending Aorta – from fusion of paired aortae - posterior to 3rd pharyngeal pouch 15) Internal Carotid Artery – narrower vessel - cranial extension of dorsal aorta - located in mesenchyme lateral to notochord - medial to ACV - seemingly broken (by pharyngeal pouch) into 2 segments - around Rathke’s pouch, @ sides of infundibulum and diencephalon 16) Jugular Ganglion – derived from neural crest cells - dark, smaller mass of cells - posterior to IX nerve - fades out w/in 4th branchial arch 17) Thyroid Rudiments – from pharyngeal floor - median diverticula/depression @ level between 1 st and 2nd pair of pharyngeal pouches 18) Oral Plate / Pharyngeal Membrane - separates stomodeum from foregut - constituted by apposition of pharyngeal endoderm and stomodeal ectoderm - ruptures to form mouth 19) Preoral Gut – small; cranial to pharyngeal membrane - becomes less conspicuous after rupture of oral plate 20) Stomodeum – slitlike space - lined by ectoderm - between 2 visceral arches next to foregut 21) Rathke’s Pouch – rudiment of anterior pituitary gland - irregular cavity - lined by cuboidal epithelium - opens into stomodeum 22) Laryngotracheal Groove – V-shaped ventralmost part of posterior part of foregut - seen @ level of 4th pharyngeal pouch when foregut elongates ventrally 23) Trachea – arises w/ the lung buds as ventrocaudal diverticulum of pharynx
- (in some sections) beneath esophagus 24) Lung Buds – paired bilateral expansion of laryngotracheal groove - (in posterior sections) beneath esophagus - (posteriolaterally) doughnut-like structure - fate: Bronchi - lead to lung bud proper 25) Pleural Cavities – lateral to lung buds; continuous w/ pericardial cavities 26) Esophagus – dorsal, rounded part of foregut - separated from laryngotracheal groove due to its constriction - (together w/ lung buds) found w/in thick mesentery of splachnic mesoderm 27) Mediastinum – mesenchymal mass where esophagus and lung buds are embedded - dorsal mesentery (mesoesophagus) + ventral mesentery (dorsal mesocardium) 28) Bulbus Cordis / Conus arteriosus / Bulbus arteriosus – indicated by endocardium and myocardium 29) Atrium - @ left; caudal to bulbus cordis - w/ blood corpuscles 30) Sinus Venosus - @ dorsal part of atrium - attached to foregut by dorsal mesocardium - separated from atrium by slight constriction - becomes continuous with common cardinal vein 31) Ventricle – fused left and right heart regions - identified by thick wall 32) Trabeculae – irregular projections of myocardium - numerous in ventricular walls 33) Common Cardinal Vein (CCV) / Duct of Cuvier - blood vessel (bv) continuous and @ side of sinus venosus - lower vessel - (upper vessel) Posterior Cardinal Vein 34) Pleuropericardial Membrane / Lateral Mesocardium – bridge of mesenchyme thru w/c CCV passes - separates pleural and pericardial cavities 35) Transverse Septum (TS) – mesenchyme incompletely separating pericardial cavity from peritoneal - encloses vein entering heart 36) Peritoneal Cavity – posterior to TS - continuous w/ pleural and pericardial cavity
37) Diencephalon – replaces mesencephalon - laterally compressed - w/ thinner walls 38) Infundibulum – in sections posterior to oculomotor nerves - long, ventral outpocketing of diencephalon 39) Optic Cup (OC) – formed by invagination of optic vesicles - not connected to diencephalon @ first sections
Mesenchymal cells aggregations outside of OC, becomes sclera & choroids
40) Retina – inner layer of optic cup - differentiate into: 1. Sensory Retina – thick layer of optic cup - next to lens vesicle 2. Pigmented Retina – thin external layer of optic cup 41) Optic Fissure / Choroid Fissure – formed by ventral invagination of optic cups and stalks - ventral gap in optic cup 42) Lens Vesicle – lens freed from superficial skin ectoderm (later forms corneal epithelium) - closed vesicle that differentiates into: 1. Elongated and centrally located cells (forms lens fibers) 2. Outer, narrower cell layer (forms lens epithelium) 43) Corneal Epithelium – single cell layer; covers lens of eye 44) Optic Stalk – thru w/c optic cups become continuous with diencephalons 45) Postcardinal Vein – bv; eventually lies dorsal to mesonephros 46) Intersegmental Vein – small bv; extensions of postcardinal vein - drain blood from dorsal organs (like somites, notochord, neural tube) 47) Stomach – medial to pleural cavities - continuous w/ esophagus 48) Dorsal Mesogaster – mesentery dorsal to stomach 49) Hepatogastric Ligament / Ventral Mesogaster – mesentery ventral to stomach 50) Ductus Venosus – has become the sinus venosus posteriorly - thick wall of mesenchyme - embedded in it are liver diverticula
51) Anterior Liver Diverticulum (ALD) / Cranial LD - @ level of stomach - above large bv (ductus venosus) 52) Duodenum – seen when ALD becomes continuous w/ foregut 53) Mesoduodenum – mesentery dorsal to duodenum 54) Hepatoduodenal Ligament / Duodenohepatic Ligament – mesentery ventral to duodenum 55) Posterior Liver Diverticulum (PLD) / Caudal LD – beneath ductus venosus; connects duodenum 56) Pronephros – small tubes - ventrolateral to dorsal aorta - Nephrostomes: opening of pronephros to coelom 57) Allantoic Vein (AV) / Umbilical Vein - @ lateral body wall - drains blood from allantois - is there diff. in size of left and right AV? 58) Telencephalon – appears in more posterior sections - cavity divisions: 1. Telocoel / Ventricle III – median; connects posteriorly to diocoele 2. 2 Diocoele / Ventricle I & II – lateral; connect to telocoel thru Foramen of Monro 59) Telencephalic Vesicles - lateral , oval-shaped evagination of telencephalon - becomes cerebral hemispheres 60) Lamina Terminalis – thin section of anterior telencephalic wall 61) Nasal/Olfactory Placodes – thickened skin ectoderm lateral to telencephalon 62) Nasal/Olfactory Pit – ectodermal invagination on sides of telencephalon - External nares: openings to outside 63) Vitelline/Omphalomessenteric Veins – 2 big bv @ level of gut - on sides of ALD
Avian liver diverticulum arise as 2 buds on the duodenum Amphibian liver diverticulum arise as ventral evagination of foregut
64) Cranial Intestinal Portal (CIP) / Anterior IP - @ level of duodenum, ventral to ductus venosus 65) Wing Buds – conical bulges on sides of body - @ level caudal to CIP - composed of core somatic mesoderm, covered by skin ectoderm - said skin ectoderm thickens laterally as apical ectodermal ridge
66) Intersegmented Arteries – small bv continuous w/ dorsal aorta 67) Urogenital System: a. Mesonephric/Wolffian Duct – tiny duct w/ thick wall on sides @ level of wing buds - far laterally & ventral to Posterior Cardinal Vein - formed by cavitaion of mesonephric duct rudiments b. Mesonephric Tubules – paired S-shaped tubules - medial to each mesonephric duct - fate: Mesonephric Kidneys c. Mesonephric Ridge – rounded bulge of dorsal body wall into the peritoneal cavity containing the mesonephros d. Subcardinal Veins – small bv beneath each mesonephric kidney 68) Leg Buds - @ level of Posterior Intestinal Portal 69) Tail Bud – undifferentiated cells - remnants of primitive streak and Henson’s Node 70) Allantois – dark mass w/ irregular sacculation - located to the right of hindgut, in the extraembryonic coelom - from splanchnopleure - store nitrogenous waste - embryonic respiratory organs of birds - connected to hindgut 71) Chorio-allantoic Membrane – beneath inner shell membrane - for respiration & absorption of calcium (for shell) 72) Yolk Sac – from splanchnopleure - overgrows the yolk - its endodermal cells digest the yolk - yolk is transported to embryo via vitelline veins 73) Chorion – outer wall of amniotic fold: ectoderm (outside) + mesoderm (inside) 74) Amnion – inner wall of amniotic fold: somatic mesoderm (outside) + ectoderm (inside) 75) Extraembryonic Coelom / Exocoel – lined by somatic mesoderm - cavity w/in each amniotic fold - continuous w/ intraembryonic coelom 76) Hindgut – lined by endoderm 77) Lateral Body Fold – (with head and tail folds) forms boundary between embryonic and extraembryonic regions
78) Cloaca – posterior part of hindgut - ventrally continuous w/ allantois - posteriorly continuous w/ mesonephric ducts
79) Cloacal Membrane / Anal Plate – double layered membrane - where ventral endoderm of cloaca fuses w/ ventral skin ectoderm - rupture to be anus 80) Caudal Intestinal Portal (CdIP) / Posterior Intestinal Portal – connects hindgut to subgerminal cavity