INTERESTING FEATURES IN HORSES, ETC. 187 



vestige of black near the heel. Not improbably this black surface 

 on the back part of the hind limbs, as I have already hinted, may 

 indicate that some ancestral form vi^.'s. plantigrade, and in changing 

 to a digitigrade descendant, a record was left of its ancestral 

 plantigradeness in this contrast of colour. I have seen the same 

 black mark on the hind legs of Collie Dogs ; and if the reader will 

 turn to the Serval of Fig. 17, he will see that the same surfaces are 

 black, which I take to be a co/i9?^^- vestige of an ancestral plantigrade 

 surface. Then, curiously enough, we find that the hind edge of the 

 metatarsus of Tragulus — a pigmy Chevrotain, allied to Pigs — is 

 naked and callous — a veritable plantar surface, without hair, 

 inherited from some plantigrade ancestor, not unlike a Pangolin, 

 whose soles are bare. In the evolution of digitigrade carnivora 

 and ruminants from plantigrade ancestors, with bare soles, this 

 surface became elevated above the ground, and in some became 

 hairy, hence the contrast of colour there in certain Cats, Dogs and 

 the Serval, while in the Tragulus it remained bare. 



