320 MAMMALS 



It is a curious and intoi-pstinfi; fact that tlie hoofed inani- 

 inals walk on the ends of their toes, which, however, are 

 incased in a horny (■ov(M-inp, called a hoof. The hoof is a 

 niodihcatiou of the skin. 



Among the odd-toed nianinials are the tapirs that live 

 in the tropical forest i-egions of both continents. They 

 resemble hogs in appearance aiul form, but have a large, 

 prehensile ui^per li|). 



The rhinoceroses, which have three toes on each foot, are 

 found in Africa and Asia. Tliey ha\-e a very thick skin 

 which, in some sp(>cies, is thi'own into folds. The snout 

 bears one or two hoi'ns (|uite different in structure and origin 

 from those of cattl(\ The Indian rhinocer'os has one horn; 

 while the black rhinoceros of Africa has two, one situated 

 in a line direetl>' b(>hind the othei'. The white rhinoceros 

 of Africa is a huge beast ri\-alcd in size among the land 

 animals by tlie elephant only. 



The horse has only one toe, but the so-called " splint 

 bones " are the existing remnants of a second and a fourth 

 toe. In the western states a remai'kable series of fossils 

 have been fovmd showing the development of the horse 

 from forms about the size of a, fox witli three toes behind 

 and four toes in front. 



The even-toed group of hoofed maiuma.ls have as their 

 lowest re|)resentative the iiippo|)otamus, of which there 

 are only two s|)ecies, both found in Afi-ica. They ha\'e 

 four toes, a huge, ungainl\' liody, and lai'ge canine teeth 

 developed int<.) tusks. They may be s(>en in large heixls in 

 the rivers of Afiica, in I he da\-tinie, apparenth' for the 

 sini|>le pleasuie of being in the wafei'. The\' can remain 

 beneath 1 he waler Inr a considerable intei\al of time, and 

 to facilitate such a, habit the nostrils can Ix^ closed In' 



