POSITION AND STRUCTURE OF HORSE 7 



the retention, of the outermost toe does not, how- 

 ever, affect the symmetry of the other three front- 

 toes of the tapir, which are arranged in just the 

 same manner as in the three-toed fore-foot of a 

 rhinoceros. 



As a whole, however, the skeleton of the fore- 

 foot of a tapir is obviously unsymmetrical, this 

 being due to the loss of the toe corresponding to 

 the human thumb, or first finger, as it should pro- 

 perly be called. And it may be noted here that this 

 first toe has disappeared from both feet in all 

 members of the odd-toed group, extinct as well 

 as living, although it is developed in certain 

 primitive members of the ungulate order, of which 

 mention is made in the sequel. 



This symmetrical development of the third toe 

 (inclusive of the supporting metacarpal in the fore 

 and the metatarsal in the hind limb) and its 

 superiority in size over either of the lateral ones, 

 when these are present, is the one great feature of 

 the skeleton by which the odd-toed ungulates, or 

 Perissodactyla, are distinguished from the even- 

 toed group, or Artiodactyla. In the latter group, 

 as is fully described in the volume on the ox, the 

 third and fourth toes are equal in size, and 

 developed symmetrically to one another on either 

 side of the vertical line between them. Conse- 

 quently, in that group the continuation of the main 

 axis of the limb is formed by the vertical line 



