CHAPTER XXVII. 



Ung u l ates, — concluded. 



Hyraces, Elephants, etc. 



With the exception of the extinct phenacodus, noticed among the ancestors of 

 the horse, the whole of the Ungulates described in the seven preceding chapters are 

 characterised by certain peculiarities in the structure of the wrist-joint. On 

 referring to the figure of the fore-foot of the titanothere on p. 152, it will be seen 

 that the bones of the two rows of the wrist are arranged alternately to one 

 another, that is to say, the bone marked I is placed immediately over the line of 

 division between the bones u and m. Moreover, none of these animals have more 

 than four toes to any one foot ; while in no case do they walk on the whole sole 

 of the foot after the so-called plantigrade fashion. Then, again, the huckle-bone, 

 or astragalus, in the ankle-joint, is always deeply grooved, as shown in the hind- 

 foot of a deer represented on p. 154, and in that of a rhinoceros on p. 455. 



On the other hand, in most of the Ungulates remaining for consideration the 

 component bones of the two rows of the wrist-joint, 

 as shown in the accompanying figure of the fore-foot 

 of an elephant, are placed directly one over the other, 

 so that the line of division between the bones I and c 

 is continuous with that between m and u, instead of 

 being placed immediately above m. And it will be 

 obvious that this type of structure is inferior from 

 a mechanical point of view to that distinguishing 

 the wrist-joint of the typical Ungulates. The existing 

 and many of the extinct Ungulates described in this 



chapter frequently have five toes on each foot, and the bones of the left fore-foot 

 .,..„„.., .,, ,. of an elephant (1 nat. size), 



not less than tour functional ones, with a rudiment —After Osbom. 



of a fifth on the fore-foot. They may likewise walk 



partly or entirely in the plantigrade manner ; while in the ankle-joint the upper 



surface of the huckle-bone is generally flat. In all respects, therefore, so far as 



foot-structure is concerned, these animals are less highly organised than the 



Ungulates of which we have hitherto treated. The sole living representatives of 



Ungulates with this generalised type of foot structure are the small hyraces, of 



which there are numerous kinds, and the two species of elephant. The latter are, 



however, the last survivors from a number of kindred animals ; and there formerly 



existed several other groups of more or less nearly -allied Ungulates which are 



now totally extinct. Beyond the generalised structure of their feet, there is but 



