THE LIMBS. 183 



end, and lying obliquely, so that the long axis has 

 its lower end directed backwards almost to the pos- 

 terior border of the limb. When all the loose epi- 

 dermis which incrnsts it to a variable extent during 

 life has been removed, the surface is seen to be ele- 

 vated above the surrounding skin and to have defi- 

 nite prominent margins, and also to be generally 

 convex, the tissue of which it is composed being 

 thicker at the middle than at the edges. The hinder 

 one is rather smaller and less elevated. Its posterior 

 margin is nearly straight or regularly convex; its 

 anterior margin is excavated in its upper third. It 

 is therefore more pointed above than below. The 

 upper end is about four inches below the point of 

 the hock (tuber calcis). The natural color of both is 

 dark slate, but when much dry epidermis collects on 

 the surface they have a lighter or yellowish appear- 

 ance. 



In all the species of asses and zebras the hinder 

 one is absent ; but the one on the fore limb always 

 exists, although in a modified form. It is broader 

 or more oval in shape, and with a smoother and 

 scarcely elevated surface. In the zebra it assumes 

 the form of a large circular flat black patch of bare 

 skin, nearly two inches in diameter. 



The signification and utility of these structures 

 are complete puzzles. Various suggestions have 



