166 THE STEUCTUEE OF THE HOESE 



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, &c. 

 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 pro- 

 duction, being covered sometimes with ridges or lamellee, 

 but more often with more or less elongated conical or 

 cylindrical projections called papillce. 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 continually 

 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, however, compen- 

 sated by the continual renewal of the tissue from the 

 surface of the derm below. 



The greater part of the limbs of the horse is covered 

 by an even coat of short hairs, but on the hinder part 

 of the last segment these are much elongated, and 

 especially at the prominence behind the joint between 

 the metapodial bone and the first phalanx of the digit, 

 where they form a considerable tuft or lock, which has 

 given the name of 4 fetlock ' (i.e., foot or feet lock) to 

 this part of the horse's limb. The amount and coarse- 



