IX 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 
Fic. 113.—Bones of the manus A, of Rhinoceros, Rhinoceros sumatrensis. x. B, of 
Pig, Sus scrofa. x}. 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 néarer than in quite 
early Tertiary times. The order Condylarthra seems to be the 
starting-point of both these sub-divisions. Huprotogonia has been 
considered to be an ancestor of the Perissodactyle branch, and 
Protogonodon or Protoselene of the Artiodactyla. If this be true, 
