FAM. 3. RHINOCEROTIDAE.--This family is to be distinguished from the preceding by a number of characters, which though not universal are general. In the first place, there are commonly horns, or a horn, consisting of what appears to be an agglomeration of hair-like structures fixed upon a roughened patch of bone on the surface of the nasals. The incisors are diminished or defective, and the upper canines are often wanting. The molars and premolars are alike. The fore-feet are four- or three-toed, but are functionally tridactyle; the hind-feet are three-toed. The skeleton in this family is massive, and the limbs relatively short. The skull, as in the Tapirs, has a confluent orbit and temporal fossa. The upper lip is generally more or less prehensile; the body is as a rule--to which the Pleistocene Hairy Rhinoceros is of course an exception--rather sparsely covered with hair. In this feature the Rhinocerotidae contrast both with the Tapiridae and the Equidae. The family in reality contains but one existing genus, though three have been instituted, viz. {254} _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 concerns 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 investigated 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_[166] this gut is furnished with numerous long cylindrical narrow outgrowths "like tags of worsted"; in the allied _Rh. sondaicus_ these tags are present, but are flatter 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[167] studied some years since the skull features which serve to differentiate the existing forms.