vi.] GENERAL VIEW OF INTERNAL SKELETON. 235 



The axial skeleton alone may, indeed, as in Serpents, serve 

 the purposes of the appendicular skeleton, and become an 

 instrument not only for climbing and swimming, but for 

 leaping, grasping, and crushing. 



We have found that both categories are always present in 

 the two highest classes (Mammals and Birds). In the Ichthy- 

 opsida we have seen that the predominance of the axial 

 skeleton may in some (as the Lamprey) be at its maximum, 

 and yet that in others the appendic- lar one may be greatly 

 developed while the axial one is extremely reduced (as in the 

 Frogs). 



It is the class of Birds which shows the greatest constancy 

 in not only the existence but in the importance both of size 

 and function of the appendicular skeleton. In them the 

 anterior part of the axial skeleton (i.e. the cervical region 

 and skull) is often modified by its great length and mobility 

 to act as an elongated prehensile limb. This function is also 

 performed by the posterior end of the axial skeleton in some 

 Reptiles (e.g. the Chameleon), and even in some beasts, of 

 man's own order (e.g. the Spider Monkeys), the tails of which 

 (as has been before said) are so prehensile as to literally serve 

 the purpose of a fifth hand. 



