ANIMAL LOCOMOTION. 51 



this obliquity. The angulation is most pronounced in the horse, 

 less so in the ox, and scarcely, if at all, in the hog. (See p. 55.) 



It is evident that the more the toes are separated the better tht 

 limb is supported. It would appear to be one of the uses of the 

 digits that they are capable of moving so as to increase the width 

 of the under surface of the foot. Such an increase of width en- 

 sues from two causes, — first, from the pressure outward of the 

 foot against the ground; and, second, from the traction of the 

 digits by the action of muscles. The muscular action is most 

 pronounced. It is well defined along the outer border of the 

 foot. As the pressure shifts across the foot from the outer to 

 the inner border, the digits leave the ground and are lifted and 

 abducted as they are relieved from duty. In the capybara the 

 movement of abduction begins before the limb reaches the ground 

 (series 746, Fig. 6). Just as the foot is lifted the inner border is 

 turned outward and the sole is disposed to the air in the position 

 of eversion, — that is to say, the sole, while directed outward, is 

 so arranged that the inner border of the foot is directed down- 

 ward and the outer border upward. As the foot is everted the 

 toes become abducted. 



Eversion is "well seen in the horse (series 622 and 633). It is pres- 

 ent, but less marked, in the deer (series 681). A good study can be 

 seen in series 619. In the slow movement of the walk the feet are 

 not everted at the moment of the removal of the weight, but after 

 the feet are well in the air. This is especially noted in series 581. 



In series 594 the figures of foreshortening show that when, as 

 in Figs. 3 and 6, the fore foot is lifted, the foot moves towards the 

 median line, and when the hind limb moves it swings off from the 

 trunk. It is likely that the greater width of the pelvis over that of 

 the withers compels the hind limb to describe an excursus outward. 



That the amount of motion inward under the body is suscep- 

 tible of modification is evident from the fact that among fast 

 pacing-horses the feet are brought inward, in order to reach the 

 same spot on the ground. Since the fore limb is the more mobile 

 of the two, it is likely that in the process of adaptation* the in- 



* The word " adaptation'' is here used in the sense that a terrestrial animal 

 possesses the power of modifying to a slight degree the movements of the 

 limbs according to the character of the ground it is moving upon. (See p. 96.) 



