THE LIMBS 



173 



ungulate, either Perissodactyle or Artiodactyle, except 

 the most ancient forms. It is, therefore, most unlikely 

 that anything of this digit should remain in the horse 

 after the complete disappearance of the second, fourth, 

 and fifth. In the next place, there is nothing beneath 

 the modified patch of skin showing any trace of the 

 structure of a toe, and the resemblance of this patch to 

 a hoof is of the very slightest character, and, indeed, in 

 the donkeys and zebras none whatever. But the most- 

 serious objection is the situation of the one that is most 

 constant — that on the fore limb — where it is placed, 

 not on the hand, as it would be if it represented the 

 thumb, but upon the fore-arm, at some distance above 

 the wrist-joint. Lastly, such a hypothesis is quite un- 

 necessary, for they obviously belong to a numerous class 

 of special modifications of particular parts of the cutan- 

 eous surface which occur in very many animals, the use 

 of which is in most cases remarkably obscure. Bare 

 spots, thickened patches or callosities, and tufts of 

 elongated or modified hair, often associated with groups 

 of peculiar glands, are very common on various parts of 

 the body, but especially the limbs, of many ungulates, 

 and to this category the 6 chestnuts' of the horse 

 undoubtedly belong. 1 



1 The apparently capricious distribution of these may be illus- 

 trated by the following diagnoses of two groups or genera into 

 which the pigmy chevrotains (small deer-like ruminants with some 

 affinities to pigs) were divided by the late Dr. J. E, Gray, and which 



