Show pageOld revisionsBacklinksBack to top This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong. ====== FOREGUT ====== ===== PRELARYNGEAL PART OF FOREGUT ===== * cephalic or pharyngeal part of foregut * funnel shaped expansion compressed dorsoventrally * dorsal wall or roof * notochord * hindbrain * pair of dorsal aorta * ventral wall or floor * ectodermal stomodaeum * forward bulging of pericardial sac * developing heart * septum transversum * two lateral walls * separated from overlying surface ectoderm by * splanchnic mesoderm * undergoes segmentation * mesodermal bars / branchial or visceral arches * Each arch contains * surface ectoderm * core of mesoderm * inner lining of pharyngeal endoderm * extends ventrally and medially * along floor or ventral wall of pharynx * meets the corresponding arch of opposite side * Between each arch * closely approximated membranes * in fishes they rupture * in terrestrial * series of ectodermal grooves called branchial or visceral cleft / ectodermal cleft * same on inner side endodermal pouches / pharyngeal pouches are formed * FIRST POUCH * dorsal part extends in to mesenchyme outwards * medial part of this recess persists as auditory tube * lateral part forms primitive tympanic cavity * mucous lining of tympanic cavity * mastoid antrum , mastoid air cells * mucous layer of tympanic membrane * the thin layer of mesoderm between First pouch and first cleft * this region forms tympanic membrane ( tridermal in nature ) * SECOND POUCH * THIRD POUCH * FOURTH POUCH * Floor of primitive pharynx * developing tongue * thyroid diverticulum * laryngo-tracheal groove * FIFTH POUCH * FIRST ARCH ( श - स - ष ) ectoderm - mesoderm - endoderm * श - * forms skin over the * upper jaw , lower jaw and tragus of auricle * स - * Artery - first aortic arch which disappears * Nerve - * pre trematic accompanies caudal border or preceeding arch * Chorda Tympani nerve * post trematic follows cephalic border of succeeding arch * Mandibular nerve * Muscle * Tensor tympani , tensor veli palatini * Muscles of Mastication , Mylohyoid * Anterior belly of digastric * Skeletal - * central axis of mesodermal core is chondrified * cartilaginous bar is enveloped by perichondrium * dorsal maxillary process * Ventral Mandibular process ( called as meckel's cartilage ) * dorsal part ossified to form * malleus and incus * ascending part regresses * fibrous part persists as * anterior ligament of malleus * sphenomandibular ligament * fibrous part is ossified to form * body of mandible * from mandibular foramen to mental foramen * SECOND ARCH * S - * Muscle - * Stapedius , stylohyoid , * Platysma , posterior belly of digastric * Auricular , epicranius * Skeletal - * Cartilaginous bar is called as reichert's cartilage * dorsal part of cartilage ossified to form * stapes * succeeding part forms * styloid process of temporal bone , stylohyoid ligament * Ventral part is converted * lesser cornu * upper part of body of hyoid bone * THIRD ARCH * S * muscle * stylopharyngeus * skeletal - * cartilaginous bar * dorsal part dissapears * ventral part is ossified * greater cornu of hyoid bone and lower part of hyoid bone * * FOURTH ARCH * S * muscle * cricothyroid * Skeletal * cartilaginous bar * dorsal part dissapears * Ventral part forms lamina of thyroid cartilage * FIFTH ARCH * DISSAPEARS * SIXTH ARCH * S * muscle * all intrinsic muscles except cricothyroid * Skeletal * Cartilaginous bar * Dorsal part dissappears * Ventral part forms cricoid and arytenoid cartilage ===== POST LARYNGEAL PART OF FOREGUT ===== * Oesophageal segment * extending from laryngeal diverticulum to fusiform dilation stomach * buds * lung buds * Gastric segment * dorsal border grows more rapidly than ventral border * greater curvature and lesser curvature * ventral border * suspended from anterior body wall by * ventral mesogastrium * by hepatic bud gets divided to form * lesser omentum * falciform and coronary ligaments of liver * dorsal border * attached to posterior body wall * dorsal mesogastrium * spleen develops * it undergoes rotation vertical axis - 90 degrees * left surface ---> ventral * left vagus supplies anterosuperior surface * right surface ---> dorsal * right vagus supplies postero inferior * Duodenal Segment * Two off shoots * liver * pancreas en/foregut.txt Last modified: 2023/06/08 12:06by 127.0.0.1