142 UNGULATA. 



OMNIVORA. 



Fam. 1. Hippopotamidce. — This group contains only the 

 single well-marked genus Hippopotamus, characterised by the 



Fig. 638. — Skull ot Hippopotatmis amphibius, side view. (After Giebel.) 



massive heavy body, the short blunt muzzle, the large head, 



and the presence of teeth of three kinds in both jaws (fig. 



2 2 



G38). The incisors are , the canines extremely large, 



, and tlie molars ' or , with crowns adapted 



1—1 7—7 G—6 



for grinding vegetable substances. The upper canines are 

 comparatively short, but the lower canines are in the form of 

 enormous tusks, with a chisel-shaped edge. The feet are 

 massive, and are terminated by four hoofed toes each. The 

 eyes and ears are small, and the skin is extremely thick, and 

 is furnished with few hairs. The tail is very short. 



The molar teeth in the Hippopotamus are of the bunodont 

 type, their crowns being tuberculated, and wearing down 

 with use so as to produce a characteristic double trefoil 

 pattern (fig. 639). The number of incisors varies, as regards 

 the lower jaw. In the living forms. Hippopotamus amphihms 

 has four lower incisors, and belongs, therefore, to a sulj- 

 generic group, which includes also most of the fossil forms, 

 and which has been called Tetraprotodon. The only other liv- 

 ing member of the family is the small Liberian Hippopotamus, 



