PHENACODUS. 



from the Phenacodus to the horse as we now know him, 

 the third digit has remained the principal one of both fore and 

 hind hmbs. It is instructive to note that the phalanges and 

 digits of the hind limb have a greater tendency to decrease in 

 number than those of the fore leg. As the fore foot is nearer 

 to the head than the hind foot, its functions are more various. 



Fig. 20I. — Phenacodus Prim^vus (yV^^ real length). 



and its digits are less liable to become affected by disuse. In 

 man, we find that the toes are smaller than the fingers ; and 

 that, in many cases, the little toe has lost its third phalanx ; 

 although the little finger still retains that bone. In the case 

 of the reappearance of the second and fourth (as in Fig. 184) 

 digits in the horse, the fore legs are far more frequently 

 supplemented in this way, than the hind ones. 



