270 



COMPARATIVE ANATOMY 



the scapula anteriorly above the gills makes its first appearance in this 

 group. 



In the head region, the visceral muscles become specialized in relation 

 to the jaws. The levators of the first two visceral arches form the jaw 



^•^BOCORACOHUMEnALI. 

 iNTESKWNCHayLARIS 



TRJC£;PS-A^4C0NE^JS 

 BICEP: 



D NECTURUS. 



EB^XIAL TRUNK MUSCLES 



3BLIQU I - EXTERNUS AND JNTERNUS 



DCPRESSOft UAhJWBULAE 

 SPHINCTER COLLI 

 TRAPEZIUS 



OOflSAUS SCAPULAE 

 LATISSIMU; 



E.SPHENODON. 



TRANSVEBSOSPINALIJ 

 LONGISSIMUS 

 LE0C04TAL1S 



UNCINATE Process 



:U1. MUSCLES 



KTKUUAL MUSCLU 



SARTORIUS 



TENSOR VACtUE FDMRtS 

 0LUTEU5 MAXIMUS 



Fig. 224. — Superficial lateral trunk muscles in an amphibian, a reptile, and a mam- 

 mal. D. Necturus, E. Sphenodon, F. Felis. The metamerism of the lateral trunk 

 muscles which is such a striking feature of the lower vertebrates is retained in urodeles 

 and reptiles, but disappears in inammals. The factors in this change are chiefly the 

 increasing dominance of the appendicular muscles and the fusion of the primarily 

 metameric embryonic trunk muscles. The primitive metamerism, however, appears in 

 mammalian einbryos. 



muscles, including the masseter, temporalis, pterygoids, while the depres- 

 sors of these arches become the intermandibularis muscles. The muscles 

 of the remaining visceral arches remain relatively unmodified. (Fig. 223.) 



