[Illustration:  Fig. 246.—­Skull of Deinotherium giganteum, greatly reduced.  From the Upper Micene of Germany.]

The true Elephants (Elephas) do not appear to have existed during the Miocene period in Europe, but several species have been detected in the Upper Miocene deposits of the Siwalik Hills, in India.  The fossil forms, though in all cases specifically, and in some cases even sub-generically, distinct, agree with those now in existence in the general conformation of their skeleton, and in the principal characters of their dentition.  In all, the canine teeth are wanting in both jaws; and there are no incisor teeth in the lower jaw, whilst there are two incisors in the front of the upper jaw, which are developed into two huge “tusks.”  There are six molar teeth on each side of both the upper and lower jaw, but only one, or at most a part of two, is in actual use at any given time; and as this becomes worn away, it is pushed forward and replaced by its successor behind it.  The molars are of very large size, and are each composed of a number of transverse plates of enamel united together by ivory; and by the process of mastication, the teeth become worn down to a flat surface, crossed by the enamel-ridges in varying patterns; These patterns are different in the different species of Elephants, though constant for each; and they constitute one of the most readily available means of separating the fossil forms from one another.  Of the seven Miocene Elephants of India, as judged by the characters of the molar, teeth, two are allied to the existing Indian Elephant, one is related to the living African Elephant, and the remaining four are in some respects intermediate between the true Elephants and the Mastodons.

[Illustration:  Fig. 247.—­A, Molar tooth of Elephas planifrons, one-third of the natural size, showing the grinding surface—­from the Upper Miocene of India; B, Profile view of the last upper molar of Mastodon Sivalensis, one-third of the natural size—­from the Upper Miocene of India. (After Falconer.)]

The Mastodons, lastly, though quite elephantine in their general characters, possess molar teeth which have their crowns furnished with conical eminences or tubercles placed in pairs (fig. 247, B), instead of having the approximately flat surface characteristic of the grinders of the Elephants.  As in the latter, there are two upper incisor teeth, which grow permanently during the life of the animal, and which constitute great tusks; but the Mastodons, in addition, often possess two lower incisors, which in some cases likewise grow into small tusks.  Three species of Mastodon are known to occur in the Upper Miocene of the Siwalik Hills of India; and the Miocene deposits of the European area have yielded the remains of four species, of which the best known are the M.  Longirostris and the M.  Angustidens.