254 VISCERA OF RAJNOCEROS CHAP. 
Rhinoceros, Ceratorhinus, and Atelodus. 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 
premolars 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- 
erowths “like tags of worsted”; in the allied Rh. sondaicus these 
tags are present, but are flatter and broader; while in the two- 
horned Rh. swmatrensis 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 Ah. indicus and 
Rh. sondaicus, but are absent in Rh. swmatrensis. 
Sir W. Flower® studied some years since the skull features 
which serve to differentiate the existing forms. 
In Rh. sumatrensis the two long downward processes of the 
squamosal 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 Garrod, Proc. Zool. Soc. 1873, p. 92; ibid. 1877, p. 707. Beddard and Treves, 
Trans. Zool. Soc. xii. 1887, p. 183. 
2 Proc. Zool. Soe. 1876, p. 443. 
