MAMMALIA. 389 



universal. In the true monkeys, all the extremities are 

 shaped like hands, and are used for prehension as well as for 

 locomotion. In the Bats, that part of the anterior extremities 

 which corresponds to the fingers of the human hand, is 

 enormously developed, and forms the bony framework of the 

 wings (Fig. 334). In the Seals (Fig. 290), the extremities 



Fig. 290. SKELETON OF SEAL.* 



are converted into paddles; and there are some warm-blooded 

 herbivorous animals inhabiting the sea, in which the hinder 

 legs are altogether wanting. 



The number of vertebra or joints in the spinal column 

 varies much in the several tribes, the difference depending 

 principally upon the presence or absence of the tail, and the 

 varying number of its parts. A remarkable uniformity pre- 

 vails in the structure of the neck. The short thick neck of 

 the Elephant, and the long slender neck of the Giraffe, contain, 

 precisely the same number of vertebra, namely, seven. This 

 is the invariable number, though there are a few apparent 

 exceptions. The mammalia present in this respect a singular 

 contrast to birds (ante p. 298), and show how in the mecha- 

 nism of the animal frame, similar results may be attained by 

 the most opposite arrangements. 



Head. The head differs greatly, not only in size and form, 

 but also in what may be regarded as its appendages. The 

 Tapir, an animal allied in many respects to the Hog, has the 



* For description, see footnote page 388. 

 VOL. it, I 



