THE SKIN AND SKELETON. 



139 



of ribs and tail, but no breast-boue ; the J'^rog has a breast- 

 bone, but neither tail nor ribs. As the skeleton of a Fisli 

 is too , complicated for the primary student, we will select 

 for illustration the skeleton of a Lion — the type of quad- 



^^ 



rnpeds. It should be remembered, however, that all "Ver 

 tebrates are formed on one plan. 



In the lowest Vertebrate, Amphioxus, the only skeleton 

 is a cartilaginous rod running from head to tail. There is 

 no skull, nor ribs, nor limbs. In the cartilaginous Fishes, 



