272 



COMPARATIVE MORPHOLOGY OF VERTEBRATES 



and cricoids. The origin of the thyreoid is best seen in the mono- 

 tremes where the hyoid apparatus enters into close relations with the 

 larynx (fig. 294), while the second and third branchial cartilages 



Fig. 293. Fig. 294. 



Fig. 293. — Laryngeal apparatus of Chelone, after Goppert. ar, arytenoid; b^~^, 

 fitst and second branchial arches; cr, cricoid; d, dilator laryngis muscle; g, glottis; h, 

 hyoid; he, hyoid cornua; sph, sphincter laryngis; tr, trachea; cartilage dotted, bone black. 



Fig. 294. — Ventral and side views of monotreme larynx, after Gegenbaur. c, 

 cricoid; h, hyoid; /, thyreoid; tr, trachea. 



Fig. 295. — Dorsal and side views of larynx of opossum, Didelphys virginianus 

 (Princeton, 1739), cartilages dotted, a, ayrtenoid; c, cricoid; e, epiglottis; g, glottis; A, 

 hyoid; t, trachea; th, thyreoid. 



form two plates, the lateral elements of the thyreoid on either side, 

 the median element of the hyoid forming a copula. In the higher 

 mammals the association of hyoid and larynx is not so intimate, 



