278 THE HORSE AND ITS RELATIVES 



character ; as the loss of side-toes is distinctly retro- 

 gressive." 



The adaptation for speed is most noticeable 

 in the progressive lengthening of the limbs, and 

 the gradual discarding of the lateral toes. The 

 limb-elongation is most marked in the lower 

 segments, more especially the foot ; the thigh- 

 bone, or femur, and the humerus, or upper bone 

 of the fore-leg, displaying much less proportionate 

 lengthening. This causes the powerful muscles 

 necessary to work the limbs to be situated close 

 to, or even within, the body ; while they act upon 

 the extremities by means of the long, slender 

 tendons, which are as tough and elastic as steel, 

 and whose development in the modern racehorse 

 is expressed in horse-dealing language as "plenty 

 of bone." Concurrently with these changes in 

 the bones of the limbs, the sole of the foot is 

 gradually raised from the ground, till eventually 

 the whole weight of the body rests on the tips 

 of the toes, whose terminal armament becomes 

 modified from a narrow claw or nail into a broad 

 hoof. Apparently, in herbivorous animals adapted 

 for running on hard ground, this elevation of the 

 sole of the foot is always accompanied by a re- 

 duction in the number of the toes, for we find 

 the same thing occurring in antelopes, deer, and 

 giraffes, although in a somewhat different fashion 

 and to a rather less marked degree. 



