ORIGIN OF PERISSODACTYLES 



199 



canines would in the same way cease to be useful, and even 

 become encumbrances to such grazing creatures ; and their dis- 

 appearance 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. x . B, of 

 Pig, Sus scrofa. x * s . 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, 



