THE TEETH OF ARTIODACTYLE UNGULATA. 331 



in old animals they are often broken off, it is not certain 

 that they are much employed in fighting. Its other teeth 

 are in no respects remarkable. 



Hippopotamus. The dental characters, as well as others, 

 indicate the affinity of the Hippopotamus to the Suidce. 



The incisors are tusk-like, and bear but little resemblance to 

 those of most other mammalia ; they are nearly cylindrical, 

 bluntly pointed at their apices by the direction of wear, 

 which is in some measure determined by the partial distri- 

 bution of the enamel, which is laid on in longitudinal 

 bands in the upper teeth, but merely forms a terminal 

 cap on the lower incisors. 



The upper, standing widely apart, are implanted nearly 

 vertically : the lower incisors, of which the median pair are 

 exceedingly large, are implanted horizontally. 



The canines are enormous teeth; the lower, as in the 

 Hog, is trihedral, and is kept pointed in the same manner ; 

 the upper canines are not so long, and the portion exposed 

 above the gum is but short. 



The incisors and canines are all alike teeth of persistent 

 growth. 



The premolars, of which the first is lost early (being 

 perhaps a milk molar like the similar tooth in the pig) 

 are smaller and simpler teeth built up on the same type 

 as the true molars. 



These latter, especially when worn, have a very charac- 

 teristic double trefoil pattern ; the four cusps, in the first 

 instance, were separated by a deep longitudinal and a still 

 deeper transverse groove; each cusp was, moreover, tri- 

 lobed; the first result of wear is to bring out the appear- 

 ance of four trefoils ; next, when the longitudinal furrow is 

 worn away, two four-lobed figures result ; and finally all 



