The Rhinoceros has no canine teeth; the incisor teeth vary, not only in regard to their form and proportions, but also their existence; and in the varieties of these teeth we may discern the same inverse relation to the development of the horns which is manifested by the canines of the Ruminants. Thus, the two-horned Rhinoceroses of Africa, which are remarkable for the great length of one or both of the nasal weapons, have no incisors in their adult dentition; neither had the great extinct hairy species (Rhinoceros tichorhinus), though that the latter had great horns is proved by the nature of the bones of the nose and face which supported their weight. The Sumatran bicorn Rhinoceros combines, with comparatively small horns, moderately developed incisors in both jaws.
The sternum of the mature animal consists of four bones, the first of which is compressed into a ploughshare-like shape, and projects in a point in front of the first rib. All the bones of the fore limbs of the Rhinoceros resemble those of the Tapir more than those of any other animal; but from their much larger size are not at all likely to be confounded with them. Of the hind limbs, the points offering peculiarities are as follows:—The femur is remarkable for being extremely flattened from before backwards, and the projection called by Cuvier the third trochanter projects very much, forming a hook ascending towards a hook which descends from the projection known as the grand trochanter, thereby leaving an oval hole between these two projections. With regard to the lower portions of the hind leg, resemblances are to be found both to the Horse and Tapir, the tibia, fibula, and tarsus being built on the same plan as those of the former, although some of the bones of the tarsus resemble those of the Tapir more than they do those of the Horse. There are also some points of resemblance in the metatarsus to that of both the Horse and Tapir. The difference between the hind legs of the Rhinoceros and Elephant is very marked, and their gait is different.
FEMUR OF RHINOCEROS.
The dentition of the Rhinoceros differs in a very remarkable degree from that of the family of Horses. The grinders are implanted by distinct roots, and in the upper jaw their crowns are traversed by two deep folds of enamel, which constitute open valleys. In the lower jaw they are composed of two crescent-shaped lobes, also open. The covering of “cement” is thin, and never fills up the valleys, as in the case of the more complex dental system in the Horse. The normal number of the grinders is seven in each jaw, while the incisors, as we have already remarked, vary, not only in form, but also are sometimes absent, and canines are not developed in any of the living or fossil members of the family.
THE AFRICAN RHINOCEROSES.
Of the number of species of Rhinoceros there is considerable doubt. At least four, possibly five, inhabit Africa, and four Asia. With regard to the African species, we will first take the large “WHITE” RHINOCEROS (Rhinoceros simus) described by Burchell. This is an animal measuring somewhat over twelve feet in length and about five feet ten inches in height. It has a square nose and two large rounded horns, the anterior one averaging about two feet six inches in length, but not uncommonly found measuring three feet six inches, sometimes even over four feet; the posterior rarely or never exceeding fifteen inches, and generally not being more than twelve inches. Its skin is smooth, and without any of those folds so characteristic of the Asiatic species. It inhabits all the country south of the Zambesi, and probably it may also exist in Central Africa. It feeds solely on grass, and sometimes collects into small herds.
DENTITION OF RHINOCEROS. A, UPPER; B, LOWER JAW.
OSWELL’S RHINOCEROS[267] in no way differs from R. simus, except that the front horn points forwards, and in some cases even downwards. This Mr. Drummond considers not to be a distinct species, but only an accidental and local variety.