THE RHINOCEROSES 



1051 



columns have completely coalesced so as to form a continuous external wall to 

 the crown; this wall being sinuous, and in some cases (as in the upper figure) 

 forming a prominent buttress at the front outer angle of the crown. From this 

 outer wall proceed two continuous, 

 oblique, transverse ridges separated 

 from one another by a deep valley, 

 interrupted by projecting processes 

 from one or both ridges, and some- 

 times also from the outer wall. This 

 middle valley is usually quite free 

 from cement; and its form, as like- 

 wise the relative height of the whole 

 crown, varies considerably in the dif- 

 ferent species. Instead of having the 

 simple, transverse ridges found in 

 those of the tapirs, the lower cheek- 

 teeth of the rhinoceroses have a pair 

 of crescents, placed one in front of 

 the other. On each side of both the 

 upper and lower jaws there are seven 

 cheek-teeth; but the last molar in the 

 upper jaw differs from the rest in 

 having its hinder ridge more or less 

 aborted, so that the form of the crown 

 is generally triangular. 



As regards their front teeth, the 

 different species of rhinocroses present 

 a considerable amount of variation, 

 some of them having such teeth in 

 both jaws, while in others they are 

 totally absent; but there are never 

 any canine teeth or tusks in the upper 

 jaw, and the number of upper incisor 

 teeth never exceeds two pairs. In 

 the lower jaw there may be a pair of 

 large, pointed and nearly horizontal 

 tusks, and between them a small pair 

 of incisor teeth. 



All the living rhinoc- 

 eroses are animals of 

 large size and heavy build, with the 

 legs comparatively short and stout, 

 although less so than in the hippo- 

 potamus. Each of the toes is furnished with a relatively-small, but broad and well- 

 defined, hoof-like nail. The head is large and elongated, with a concave profile, and 



LEFT UPPER MOLAR TEETH OF TWO EXTINCT 

 SPECIES OF RHINOCEROSES. 

 (Both considerably worn by use.) 



