THE LIMBS. 185 



very many animals, the use of winch 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 es- 

 pecially the limbs, of many ungulates, and to this 

 category the " chestnuts " of the horse undoubtedly 

 belong.* 



If they teach us nothing else, they afford a valu- 

 able lesson as to our own ignorance, for if we cannot 

 guess at the meaning or use of a structure so con- 

 spicuous to observation, and in an animal whose 

 mode of life more than any other we have had 

 the fullest opportunity of becoming intimately ac- 

 quainted with, how can we be expected to account 

 off-hand for the endless strange variations of form 

 or structure which occur among animals whose lives 

 are passed in situations entirely secluded from hu- 



* The apparently capricious distribution of these may be 

 illustrated 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 in all other respects closely resemble each 

 other. (1) Mcminna. "Chin entirely "covered with hair. 

 Hinder edge of the metatarsus covered with hair, with a large, 

 smooth, naked prominence on the outer side rather below the 

 hock." (2) Tragulus. " Throat and chin nakedish, subglan- 

 dular, with a callous disk between the rami of the lower 

 jaw, from which a band extends to the fore part of the chin. 

 Hinder edge of the metatarsus naked and callous." 



