THE LIMBS. 177 



surface. Over the greater part of the skin it forms 

 an exceedingly thin layer, which, nevertheless, serves 

 as a protection to the softer and more sensitive derm 

 below ; but in certain parts it accumulates in solid 

 masses of various forms, constituting the hairs, 

 horns, nails, claws, hoofs, etc. Wherever these great 

 accumulations take place, the superficial part of the 

 derm is specially modified so as to afford a larger 

 vascular surface available for their production, being 

 covered sometimes with ridges or lamellce, but more 

 often with more or less elongated conical or cylin- 

 drical projections called papittce. Each hair grows 

 on such a papilla, which is sunk in the bottom of a 

 follicle or deep pit in the derm or true skin. Under 

 whatever form it appears, the epidermis is continu- 

 ally being removed at the surface, flaking or peeling 

 off in minute fragments, or being worn and ground 

 away by the contact of external substances, or, as in 

 the case of hairs, cast off entire. The loss is, how- 

 ever, compensated by the continual renewal of the 

 tissue from the surface of the derm below. 



The greater part of the limbs of the horse is cov- 

 ered by an even coat of short hairs, but on the 

 hinder part of the last segment these are much elon- 

 gated, and especially at the prominence behind the 

 joint between the metapodial bone and the first pha- 

 lanx of the digit, where they form a considerable 



