LUNGS AND AIR DUCTS 



271 



branchial arches, serves as dilatators of the glottis; the others, con- 

 nected with the laryngeal cartilages themselves, constrict the open- 

 ing. In the anura the cricoid is converted into a ring, with the 

 arytenoid hinged within and anterior to it, the whole larynx moving 

 anteriorly to a position between the hinder processes of the hyoid 

 plate (fig. 292). Inside of the short larynx thus framed by these 

 cartilages are a pair of folds of the laryngeal lining, the vocal cords, 

 extending parallel to the margins of the glottis. These may be 

 tightened or relaxed, and by their vibration of their edges under 

 influence of the breath the voice is produced. 



Fig. 291. — Trachea, etc., of i4m/>Ai- Fig. 292. — Laryngeal cartilages of 



uma, after Wilder, a, arytenoid carti- frog, after Gaupp. a, arytenoid; c, 



lages; b*, fourth branchial arch; dtr, cricoid; A, posterior part of body of hyoid; 



dilatator tracheae muscle; hp, hyo- /,hyo-cricoid ligament; ^/, tracheal proc- 



pharyngeus muscle; /, lung; /r, trachea ess of cricoid; /, thyreoid; process of 



with cartilages in its walls. hyoid. Cartilages dotted one black. 



The larynx is scarcely more developed in reptiles. The cricoid is usually an 

 incomplete ring, to which the arytenoide are attached, and the whole is placed 

 just ventral to the median part of the hyoid, with which it is closely associated 

 (fig. 293). In several reptiles a fold of the mucous membrane just in front of 

 the glottis is supposed to represent the beginnings of an epiglottis (infra), while 

 in geckos and chameleons a pair of folds, running dorso-ventrally in the larynx, 

 serve as vocal cords. The larynx is also rudimentary in the birds, its place as a 

 vocal organ being taken by the syrinx to be described below, in connexion with 

 the trachea. The arytenoids are frequently ossified in birds. 



In the mammals the larynx reaches its highest development. Its 

 framework is formed by the arytenoid and cricoid cartilages, homolo- 

 gous with those of the lower groups, and in addition, a thyreoid 

 cartilage (or cartilages) on the dorsal side, anterior to the arytenoids 



