CHAPTER XXI 



WHITE OR SQUARE-MOUTHED RHINOCEROS 



Ceratotheriuvi 



Ceratotherium Gray, 1867, Proc. Zool. Soc, p. 1027; type Rhinoceros simus. 



The white rhinoceros, hke the black, represents a dis- 

 tinct type of which it is the sole living member. In fact, 

 it is the most highly specialized form living. Its extreme 

 specialization is brought about by the lengthening of the 

 skull until it has become remarkably dolichocephalic or 

 long-headed. The teeth are quite as specialized as its 

 skull, and in some respects parallel those of horses. Like 

 the horses, the crowns have become very long or hypso- 

 dont, and the cement layer has grown in thickness until 

 it forms an important part of the grinding surface of the 

 teeth. The teeth are no longer composed of loops which 

 are separated by deep valleys and are open on the inside, 

 but the loops have united and enclose the cement layer 

 as islands or fossettes in the tooth. The crown is per- 

 fectly flat and shows a complicated pattern of alter- 

 nating folds of enamel, dentine, and cement. This tooth 

 specialization has been brought about by the grass diet, 

 the lengthening of the crowns and their increased surface 

 being necessary in order to masticate the tough grass stems 

 which form the chief part of their food. The dental appa- 

 ratus of the other living species of rhinoceroses, which are 

 chiefly browsing animals, consists of short-crowned teeth, 



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