254 VISCERA OF RHINOCEROS CHAP. 



Rhinoceros, Ceratorhinus, and Atelodvis. As there are so few 

 existing species the subdivision of animals which agree in so 

 many and such highly -characteristic features seems to be an 

 unnecessary procedure. The existing Rhinoceroses are but a 

 fragment of the total number of known forms from past epochs. 

 The family is very markedly on the wane. 



The genus Rhinoceros is characterised by its heavy build and 

 thick, almost smooth, skin smooth, that is to say, so far as con- 

 cerns the slight development of hair which is often thrown into 

 folds. There is one or, there are two horns on the fore-part of 

 the head, which are, as has already been pointed out, structures 

 sui generis, and not exactly comparable with the horns of other 

 living Ungulates. There are three nearly equal toes on both 

 fore- and hind-limbs. The canine teeth of existing species have 

 disappeared ; the incisors are, or are not, present ; the molars and 

 prernolars are three and four in each half of each jaw. 



The visceral anatomy of the Rhinoceros has been much inves- 

 tigated so far as concerns the Asiatic forms. A curious feature, 

 which serves to discriminate some of the Asiatic species from 

 others, is to be seen in the small intestine. In Rh. indicus * 

 this gut is furnished with numerous long cylindrical narrow out- 

 growths " like tags of worsted " ; in the allied Rh. sondaicus these 

 tags are present, but are natter and broader ; while in the two- 

 horned Rh. sumatrensis there are no tags at all, but only smooth 

 valve-like folds. Another mark by which these species can be 

 distinguished depends upon the variation in the presence or 

 absence of certain glands imbedded in the integument of the foot 

 the so-called " hoof glands." These occur in Rh. indicus and 

 Rh. sondaicus, but are absent in Rh. sumatrensis. 



Sir W. Flower 2 studied some years since the skull features 

 which serve to differentiate the existing forms. 



In Rh. sumatrensis the two long downward processes of the 

 squarnosal bone, termed respectively post-glenoid and post- 

 tympanic, do not unite below the auditory meatus. In this the 

 species in question agrees with the African forms but not with 

 the one-horned Asiatic species, where the two processes completely 

 fuse. Again, another character, though perhaps less important, 



1 Garrorl, Proc. Zool. Soc. 1873, p. 92 ; ibid. 1877, p. 707. Beddard and Treves, 

 Trans. Zool. Soc. xii. 1887, p. 183. 



2 Proc. Zool. Soc. 1876, p. 443. 



