158 THE STRUCTURE OF THE HOESE. 



and two edges and borders. The surfaces are dor- 

 sal, which in the ordinary position of the feet of most 

 mammals is turned forwards or upwards (the " back " 

 of the human hand), and ventral, or palmar in the 

 fore limb or plantar in the hind limb, turned back- 

 wards or downwards. The edges are external (ulnar 

 in the fore and fibular in the hind limb) and internal 

 (radial in the fore and tibial in the hind limb). 



The flexure between the middle and distal seg- 

 ments of the limb is called the " wrist- joint " and 

 " ankle-joint " in the fore and hind limbs respectively 

 in man, which correspond with those called the 

 "knee" and the "hock" in the horse. 



These are the essential characters in which the 

 fore and hind limbs resemble each other. Of the 

 differences many are merely adaptive to the different 

 purposes to which they are put. The perfect effi- 

 ciency of action, even in those that bear the closest 

 resemblance, is secured by a partial rotation on its 

 axis of each from the shoulder or hip, as the case may 

 be, so that the outer side of the hind limb at the uext 

 joint comes to correspond with the inner side of the 

 fore limb ; but, owing to a second rotation in the 

 middle segment in the latter, the last segments, or 

 hand and foot, are brought again into corresponding 

 positions in the ordinary walking attitude, the first 

 (radial and tibial) digits being on the inside edge, and 



