CLASS AMPHIBIA 



493 



FIG. 418. Skeleton of the frog. A, skull and vertebral column, dorsal 

 surface. B, skull and vertebral column, ventral surface. C, side view of 

 urostyle; bristle passes through opening of loth spinal nerve. D, visceral 

 arches, ar, neural arch; av, atlas; c, centrum; ex, exoccipital; fm, foramen 

 magnum; H, basilingual plate; Ha, hyoid arch; Hp, thyrohyal; mx, maxilla; 

 na, nasal; O, orbital fossa; pal, palatine; par, parasphenoid; pf, parieto- 

 frontal; pmx, premaxilla; pro, prootic; pig,' pterygoid; qj, quadratojugal; 

 sp. et, sphenethmoid; sq, squamosal; trv, transverse process; ur, urostyle; 

 vo, vomer; zyg, zygopophysis (From Bourne, after Ecker.) 



