Amongst the Even-toed or Artiodactyle Ungulates, we for the first time meet with examples of the Hippopotamus, with its four-toed feet, its massive body, and huge tusk-like lower canine teeth.  The Miocene deposits of Europe have not hitherto yielded any remains of Hippopotamus; but several species have been detected in the Upper Miocene of the Siwalik Hills by Dr Falconer and Sir Proby Cautley.  These ancient Indian forms, however, differ from the existing Hippopotamus amphibius of Africa in the fact that they possessed six incisor teeth in each jaw (fig. 244), whereas the latter has only four.

[Illustration:  Fig. 244.—­a, Skull of Hippopotamus Sivalensis, viewed from below, one-eighth of the natural size; b, Molar tooth of the same, showing the surface of the crown, one-half of the natural size:  c, Front of the lower jaw of the same, showing the six incisors and the tusk-like canines, one-eighth of the natural size.  Upper Miocene, Siwalik Hills; (After Falconer and Cautley.)]

Amongst the other Even-toed Ungulates, the family of the Pigs (Suida) is represented by true Swine (Sus Erymanthius), Peccaries (Dicotyles antiquus), and by forms which, like the great Elotherium of the American Miocene, have no representative at the present day.  The Upper Miocene of India has yielded examples of the Camels.  Small Musk-deer (Amphitragulus and Dremotherium) are known to have existed in France and Greece; and the true Deer (Cervidoe), with their solid bony antlers, appear for the first time here in the person of species allied to the living Stags (Cervus), accompanied by the extinct genus Dorcatherium.  The Giraffes (Camelopardalidoe), now confined to Africa, are known to have lived in India and Greece; and the allied Helladotherium, in some respects intermediate between the Giraffes and the Antelopes, ranged over Southern Europe from Attica to France.  The great group of the “Hollow-horned” Ruminants (Cavicornia), lastly, came into existence in the Miocene period; and though the typical families of the Sheep and Oxen are apparently wanting, there are true Antelopes, together with forms which, if systematically referable to the Antilopidoe, nevertheless are more or less clearly transitional between this and the family of the Sheep and Goats.  Thus the Paloeoreas of the Upper Miocene of Greece may be regarded as a genuine Antelope; but the Tragoceras of the same deposit is intermediate in its characters between the typical Antelopes and the Goats.  Perhaps the most remarkable, however, of these Miocene Ruminants is the Sivatherium giganteum (fig. 245) of the Siwalik Hills, in India.  In this extraordinary animal there were two pairs of horns, supported by bony “horn-cores,” so that there can be no hesitation in referring Sivatherium to the Cavicorn Ruminants.  If all these horns