canines would in the same way cease to be useful, and even become encumbrances to such grazing creatures; and their disappearance is one of the salient features in the history of the Ungulata, that is of the modern representatives of the order. The extraordinary hypertrophy of these teeth in such a line as that of the Amblypoda, which has left no descendants, was one of the reasons perhaps for the decay of those great pachyderms of mid-Tertiary times; their excessive armature became an encumbrance, since it was not accompanied by improvements in other necessary
Fig. 113.—Bones of the manus A, of Rhinoceros, Rhinoceros sumatrensis. × 1⁄5. B, of Pig, Sus scrofa. × ⅓. Letters as in Fig. 112. (From Flower's Osteology.)
directions. Some of the features of the Tertiary Ungulates have, however, been dealt with in our general sketch of the mammalian life during that epoch, and need not be again referred to here. Of existing Ungulates there are no clear indications of the descent of the Elephants or of the Hyracoidea. Their structure proclaims these two divisions to be of ancient descent, and not to be modern twigs of the Ungulate stem. As to the Perissodactyla and the Artiodactyla we cannot bring them together nearer than in quite early Tertiary times. The order Condylarthra seems to be the starting-point of both these sub-divisions. Euprotogonia has been considered to be an ancestor of the Perissodactyle branch, and Protogonodon or Protoselene of the Artiodactyla. If this be true,
