704 



MANUAL OF ZOOLOGY. 



Fig. 400. Skull of Hippopotamus amphibius , side-view. 

 (After Giebel.) 



Besides these there is an extensive series of fossil forms com- 



mencing in the Eo- 

 cene or Lower Ter- 

 tiary period, and 

 in many respects 

 filling up the gaps 

 between the living 

 forms. 



OMNIVORA. 



Fdm. i. Hippo- 

 potamidce. This 

 group contains 

 only the single ge- 

 nus Hippopotamus ', 

 characterised by 

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

 and the presence of teeth of three kinds in both jaws (fig. 400). 

 The dental formula of the living Hippopotamus amphibius is 



. 2 2 i i 4 4 i * 



t - : c -- : pm - " ; m - = = 40. 

 2-2 i i 44 33 



The incisors are nearly horizontal, those of the centre of the lower 



jaw being long and tusk-like. 

 The canines are greatly devel- 

 oped, those of the upper jaw 

 being comparatively short, while 

 the lower canines are in the 

 form of enormous tusks, with 

 a chisel - shaped edge. The 

 crowns of the prsemolars and 

 molars exhibit a characteristic 

 double - trefoil pattern. The 

 legs are very short, with mas- 

 sive feet, terminated by four 

 hoofed toes each (fig. 401). 

 The eyes and ears are small, 

 and the skin is extremely thick, 

 and is furnished with few hairs. 

 The tail is very short. 



II 



v. 



Several extinct species of 

 Hippopotamus are known ; but 

 there is only one familiar liv- 

 ing form, the Hippopotamus 

 amphibius or River-horse, and this is confined to the African 



Fig. 401. Left fore-foot of Hippopotamus 

 amphibius. (After Cuvier.) 



