The Frog: A Representative Vertebrate 57 



upper jaw (Fig. 12) is composed of three pairs of bones: the pre- 

 maxillae, the maxillae, and the quadrat ojugals. The first two bear the 

 teeth. The lower jaw is formed on each side of a pair of cartilaginous 

 rods known as Meckel's cartilage which are enclosed by the paired 

 dentary and angulosplenial bones. Attaching the jaws to the cranium 

 are the squamosals, the pterygoids and the palatines. 



PB£MAXILUV 



VOMtRINE TEETH 

 SPHENETHMOID 



PARA SPHENOID 



PTtnvcoio 



OUAORATOJUGAL 

 OCCriTAL CONDYLE 



FRONTOPARIETAL 



SOUAMOSAL 



flUAORATt 



CARTILAGE 



FORAMEN MIGNUM 



Fig. 12. — Ventral view of skull of bullfrog. 



MCNTOMCCKQ-IAN 



»NTB»IO« HORN 



ANGULOSPLENIAL 



POSTERIOR HORN 



.OEMTAKY 



HYOIO PLATt 



Fig. 13.— Lower jaw and hyoid of the bullfrog. 



The vertebral column of the frog consists of nine separate verte- 

 brae which terminate in a long, relatively thin urostyle. This column 

 of vertebrae is quite different from that of most other vertebrates as 

 it is very short and scarcely flexible. Each vertebra is similar to 

 every other one. Each consists of a heavy ventral centrum and a 

 dorsal neural arch which terminates in a short spine. The spinal cord 

 passes through the neural arches. On either side of each vertebra is 

 a broad transverse process for muscle attachment. On each end of 

 the individual vertebra is a pair of articulating processes, the .^ja- 

 pophyses that join the vertebrae to one another. No ribs are present. 



