Pharyngeal arches V and VI (unnamed) are never seen in humans. Their corresponding aortic arches, however, do occur. The muscle mass of arch V forms some of the intrinsic muscles of the larynx, which are supplied by the recurrent or inferior laryngeal branch of the vagus nerve (X)
The cartilages of arches IV and V become the framework of the larynx
The thyroid cartilage originates from both arches IV and V
The cricoid, arytenoids, the rings of the trachea, and the bronchi are formed from arch VI
Arch VI is distinctly differentiated, whereas V is transitory
AT 8 mm, ARCH II develops more rapidly than the others and overlaps the other arches caudally. This process is further accentuated by the flexion of the head at this stage of development
AT ABOUT 13 mm (about 34 days), ARCH II has entirely overlapped arches III and IV. It also has closed the second, third, and fourth pharyngeal clefts to form the cervical sinus. Only the first pharyngeal cleft persists, and by day 42, it is seen as the external auditory meatus, the only exterior evidence of the pharyngeal system