Brachial arches:-
Brachial arches also known as pharyngeal arches are mesodermal thickenings in the wall of cranial most part of foregut,the first arch is called mandibular arch, and second arch is the hyoid arch,the rest of the arches third,forth & sixth arches do not have special names,i don't mention 5th arch here because it disappers soon after formation,so the only 1st and 2nd arches have special names.
let us talk about the first arch,it is the only arch in the human embryo having double innervation,that is the 1st arch got dual nerve supply,firstly Chorda tympani that is a branch of the facial nerve is the pretrematic nerve,&,the mandibular nerve is the post-trematic nerve,i think you don't have problem to remember this,now lets talk about arterial supply of first arch,artery that supply the first arch is Maxillary artery,here is little introduction for maxillary artery,The maxillary artery,which is the larger of the two terminal branches of the external carotid artery, arises behind the neck of the mandible, and is at first imbedded in the substance of the parotid gland; it passes forward between the ramus of the mandible and the sphenomandibular ligament, and then runs, either superficial or deep to the lateral pterygoid muscle, to the pterygopalatine fossa.
It supplies the deep structures of the face, and may be divided into mandibular, pterygoid, and pterygopalatine portions,lets come back to our topic,now m talking about the muscles derived from 1st arch,these are the muscles of mastication which include masseter,temporalis,medial & lateral pteryoids,along with the muscles of mastication some other muscles like mylohyoid,anterior belly of digastric,tensor tympani & tensor palati also derived from the first arch.
Cartilage of the first arch is known as Meckel's cartilage,it got dorsal and ventral part,dorsal part gives rise to incus and malleus; while the ventral part gives rise to sphenomandibular ligament and anterior ligament of malleus.
2nd arch:-
nerve of second arch is facial nerve , while the artery is stapedial artery.
muscles derived from 2nd arch are:-stapedius,stylohyoid,posterior belly of digastric muscle,platysma,muscles of face,auricular muscles and occipitofrontalis.
cartilae of second arch is Reichter's cartilage while that of 1st arch is meckel's cartilage.Reichter's cartilage gives rise to 5s:-stapes,stylohyoid ligament,styloid process,smaller cornu of hyoid and superior part of body of hyoid.
3rd arch:-
nerve of third arch is glossopharyngeal nerve.
muscle derived from third arch is stylopharyngeus muscle.
cartilage of third arch forms greater cornu & lower part of body of hyoid bone.
4th arch:-4th arch got its nerve supply from superior laryngeal nerve.
6th arch:-the nerve of 6th arch is recurrent laryngeal nerve.
4th & 6th arches together gives rise to muscles of larynx,pharynx and soft palate.
After the formation of pharyngeal arches the region of the neck is marked on the outside by a series of groove or ectodermal clefts.
Dorsal part of first cleft gives rise to epithelial lining of external auditory meatus while ventral part of 1st cleft obliterates.
2nd arch grows much faster then the 3rd, 4th and 6th arches,so overhangs them creating a space in between called the cervical sinus.Persistence of this sinus may give rise to brachial cyst.
Lastly the endodermal pouches form the following organs:-
Ventral part of 1st pouch forms tongue.
Dorsal part of 1st and 2nd pouch forma the tubotympanic recess,which forms the eustachian tube & middle ear cavity.
Ventral part of 2nd pouch forms the tonsils.
3rd pouch forms the thymus & inferior parathyroid gland.
4th pouch forms superior parathyroid glands & parafollicular C-cells of thyroid.
embryology of diaphragm:-it is form by the fusion of septum transversum (forming the central tendon),dorsal oesophageal mesentry,the pleuroperitoneal membrane & body wall.
embryology of thyroid gland:-it develops from thyroglossal diverticulum,which pushes out from the tongue at the foramen caecum.it descends to its definitive position in the neck & losses all connections with its origin.
this development accounts for the occasional occurence of lingual thyroid,thyroglossal cyst or sinus along the path of descent.
aortic arches & their derivatives:-
common arterial trunk gives rise to "Truncus arteriosus" which forms six pairs of aortic arches out of which first,second & fifth arch disappears.
third arch gives rise to carotid arteries.
right fourth arch forms brachiocephalic & right subclavian arteries.
left fourth arch forms aortic arch & left subclavian artery.
sixth arch gives rise to riht &left pulmonary arteries & ductus arteriosus.
Derivatives of foregut , midgut & hindgut:-
Foregut:-supplied by coeliac artery.
*part of floor of mouth , including the tongue.
*pharynx.
*Derivatives of phayngeal pouches & thyroid.
*oesophagus & stomach.
*Duodenum:ascending (2nd) part up to major duodenal papilla.
*Liver , pancreas,biliary channels.
&* respiratory system.
Midgut:-supplied by superior mesenteric artery.
*from descending (2nd) part of duodenum distal to major papilla to the right two-third of transverse colon.
Hindgut:-supplied by inferior mesenteric artery.
*from left one-third of transverse colon to upper part of anal-canal.
*parts of the urogenital system derived from the primitive urogenital sinus.
derivatives of dorsal mesogastrium:-greater omentum,gastrosplenic ligament , gastrophrenic ligament & lienorenal ligament.
derivatives of ventral mesogastrium:-lesser omentum,falciform ligament,coronary ligament,right & left triangular ligament.
