340 EVOLUTION OF THE HORSE. 



a sound proof that this kind of conformation is conducive 

 to speed. 



Although, as regards the number of toes, the horse's foot 

 is better suited than that of any other animal for the develop- 

 ment of a high rate of speed ; the fact remains that the four- 

 toed cheetah {see PI. 2), hare, wild dog, and wolf, and the 

 two-toed black buck {see PI. i) are comparatively, for their 

 size, if not actually, faster than any wild horse or ass. Here we 

 have an instance of the complex nature of physical faculties, 

 which, like speed, are not made up of one component, but of 

 many. In the cat, dog and hare, the muscles of progression are 

 of much greater comparative length than those of the horse ; as 

 we may judge by the way the hocks and knees are " let 

 <lown." Although these joints in the antelope are "high off 

 the ground," the extreme length of his limbs compensates him 

 for this disadvantage, as well as that of having two toes on 

 each foot. In the case of the ancestors of this fleet ruminant, 

 the tendency to place weight both on the third and fourth toe 

 was so evenly distributed on these two digits, that the balance 

 between them has remained practically undisturbed for ages, 

 and under modifying conditions which have nearly doubled 

 the comparative length of the limbs. 



Like the horses of the present day, the members of the 

 Hipparion gracile tribe differed a good deal among each other 

 as regards conformation, as we may see by the respective 

 cannon-bones shown in A and B of Fig. 203. 



The Horse of the Future. — The bones of the limbs, 

 as we have seen, are gradually assuming the character of a 

 single column, and are increasing the rigidity of their con- 

 nections between the joints necessary for locomotion. We 



