348 



COMPARATIVE ZOOLOGY 



There is no skull, nor ribs, nor limbs. In the carti- 

 laginous fishes, the backbone is only partially ossified. 

 But usually it consists of a number of separate bones, 



called vertebra, arranged along the axis of the body. 

 They range in number from 10 in the frog to 305 in 

 the boa constrictor. The skull, with its appendages, 

 and the vertebrae, with the ribs and sternum, make 



