AIR-TUBES AND LARYNX 287 



(comp. p. 285) . In all other Mammals the thyroid is impaired , though 

 still showing traces of its primary paired nature, and it becomes 



I.. L 



Ill 



V 



tr. 



FIG. 233. DIAGRAM TO ILLUSTRATE THE METAMORPHOSIS DURING DEVELOP- 

 MENT OF THE FIRST TO FIFTH VISCERAL SKELETAL ARCHES (I V) IN 

 MAN. 



From the proximal end of the first arch (Meckel's cartilage) two of the auditory 

 ossicles, the malleus and incus (mb and in) are represented as arising, p, pinna - T 

 pr, mastoid process of skull. 



From the second arch (hyoid) arise proximally the styloid process (p.s), distally 

 the anterior (lesser) cornu of the hyoid (c.a) and a portion of the basi-hyoid (b.s). 

 By far the greater portion of this arch becomes the stylo-hyoid ligament (l.g). 

 (Concerning the stapes (*t] comp., p 101). 



The third (first branchial) arch gives rise to the greater part of the body (b.s) 

 and the posterior or greater cornu of the hyoid (c.p. ). 



The fourth (second branchial) arch gives rise to the upper segment (th f ) of the 

 thyroid cartilage, and the fifth (third branchial) to the lower one (th' 1 ). The 

 arytenoid cartilage (ar) is probably a derivative of the fifth arch, tc, cartilago 

 triticea ; cr, cricoid cartilage ; tr, trachea. 



separated from the hyoid : it is shield-shaped, and surrounds the 

 lateral and ventral regions of the larynx, overlappiug the cricoid 



