POSITION AND STRUCTURE OF HORSE 47 



event of the former not being a foot-pad, the same 

 will hold good for the latter. 



A third, and perhaps stronger objection may 

 be urged against the foot-pad theory. On the 

 assumption that the chestnuts of the existing 

 members of the Equidce are vestiges of foot-pads, 

 it is clear that these structures must have existed 

 in the ancestors of that family since the time when 

 such ancestors walked on the entire sole of the 

 foot, in the plantigrade fashion ; but, so far as I 

 know, no ungulate was ever wholly plantigrade in 

 both feet ; the nearest approach to this condition 

 obtaining in the Lower Eocene Coryphodon, in 

 which the hind-limb was wholly plantigrade, while 

 the front one was partially digitigrade. It has thus 

 to be assumed, on the foot-pad hypothesis, that the 

 front-chestnuts of the horse have been functionless 

 structures from a period antedating the evolution of 

 the Ungulata. Such a persistence, on exposed parts 

 of the body, of a functionless structure seems im- 

 probable, especially when the modifications are 

 borne in mind which, on this hypothesis, the horse- 

 line must have undergone since the time when the 

 chestnuts were functional structures. Perhaps the 

 case of the ergot may be cited against this argu- 

 ment ; but it should be remembered that this 

 structure probably acted as a functional pad at a 

 later stage of evolution than could have been the 

 case with the chestnuts. 



