Medicine and Health related Information

After the formation of pharyngheal arches the region of the neck is marked on outside by series of grooves or ectodermal clefts.

1) The dorsal part of 1st cleft develops into epithelial lining of the external auditory meatus.
2) The pinna is formed from a series of swellings, which arise on the 1st and 2nd arches, where they adjoin the 1st cleft. The ventral part of this cleft is obliterated.
3) The 2nd arch grows much faster than the succeeding arches and comes to overhang them.
4) The space between the overhanging 2nd arch, 3rd arch, 4th and 6th arches is called cervical sinus. Subsequently the lower overhanging border of the 2nd arch fuses with tissues caudal to the arches. The side of the neck thus becomes smooth.
5) The cavity of cervical sinus is obliterated, part of it may persists and give rise to swellings that lie in the neck along the anterior border of sternocleidomastoid.
6) These are called bronchial cysts, if such a cysts opens on the surface, it is called BRONCHIAL SINUS.