328 



AMPHIBIA 



xii. 14 



14. The skull of modern Amphibia 



Modern amphibia share several cranial features that distinguish 

 them from typical labyrinthodonts. The number, extent, and thick- 

 ness of the dermal elements are greatly reduced so that the otic 



b p. 



Fig. 195. Skull of the frog. a. Ventral view. b. Side view. 



ac. anterior cornu of hyoid ; art. articular ; as. angulosplenial ; col. columella auris ; d. dentary ; 

 ex. exoccipital ; fp. fronto-parietal; m. maxilla; m.m. mento-Meckelian; n. nostril; na. nasal; 

 pa. palatine; par. parasphenoid; pc. posterior cornu of hyoid; pm. premaxilla; pro. pro-otic; 

 pt. pterygoid; q. quadrate; qj. quadrato-jugal; se. sphenethmoid; sq. squamosal; v. vomer; 

 //, IX, and A', nerve foramina. (After Marshall, The Frog, Macmillan.) 



capsules are generally exposed. The orbits and interpterygoid vacui- 

 ties are large, the mandibular ramus is short and the skull as a whole 

 much flattened. The occiput is shortened so that the hypoglossal nerve 

 emerges behind the skull and (with the few exceptions noted below) 

 the parietal foramen has been lost. 



The skull of the frog (Fig. 1 95) shows great reduction and specializa- 

 tion from the early amphibian type. It may be considered as consisting 

 of a series of cartilaginous boxes or capsules, in whose walls some 

 ossifications occur, partly covered by dermal bones. The cartilaginous 



