THE SKIN AND SKELETON. 



139 



of ribs and tail, but no breast-bone ; the Frog has a breast- 

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

 is too complicated for the primary student, we will select 

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



rupeds. It should be remembered, however, that all Ver- 

 tebrates are formed on one plan. 



In the lowest Vertebrate, Arnphioxus, the only skeleton 

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

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



