206 THE MAMMALIA. 



reduced, on the hind- foot the lateral (M c 4) is the 

 least reduced, as even Hensel pointed out. Now 

 cases of atavism are not unfrequently met with in 

 the horse, where the medial splint bone on the 

 fore-foot has a digit more or less distinctly de- 

 veloped. And as the hoof of this second digit never 

 touches the ground, and, accordingly, is not worn 

 off in any way, the horn- substance becomes long 

 and irregular, precisely as in the case of the lateral 

 toes (the second and fifth) in old cows. Atavisms 

 of this kind on the hind- foot are of extremely rare 

 occurrence. 



* When it was said above that the horse no longer 

 shows any trace of rudimentary toes, this is not 

 altogether correct ; the rudimentary hoofs do still 

 exist. Thus the so-called " chestnut," a flat horny 

 wart on the skin above the carpus, seems to corre- 

 spond to the hoof of the lost thumb ; at all 

 events, I found it in cases where a second digit 

 existed. Another formation that must be included 

 here, is the so-called " spur." This spur is a small 

 cylindrical horny substance, which in our present 

 horse is concealed by the hairy tufts of the fetlock. 

 It seems to represent the coalesced horn- shoe of 

 the rudimentary second and fourth toe of the 

 horse. 



