CHAPTER XXVII 



THE UNGULATES 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 

 characterized by certain peculiarities in the structure of the wrist joint. On 

 referring to the figure of the fore-foot of the titanothere on p. 742, 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 / is placed immediately over the line of division be- 

 tween the bones u and in. 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. 744, and in that of a rhinoceros on p. 1042. 



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 / 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 

 THE BONES OF THE LEFT FORE- chapter frequently have five toes on each foot, and 



FOOT OF AN ELEPHANT. . i .-, r r ,. , ... ,. 



(One-eighth natural size.) DOt leSS thatl f Ur functlonal ones > wlth a rudiment 



(After osbom.) ^ a ^^ tn on tne 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 in generally flat. In all re- 

 spects, therefore, so far as foot structure is concerned, these animals are less-highly 

 organized than the Ungulates of which we have hitherto treated. The sole living 

 representatives of Ungulates with this generalized type of foot structure are the 

 small hyraces, of which there are numerous kinds, and the two species of elephants. 

 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 generalized structure of their feet there 

 (1106) 



