Table of Contents
FOREGUT
PRELARYNGEAL PART OF FOREGUT
POST LARYNGEAL PART OF FOREGUT
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