THE LIMBS 



165 



The Warts or Callosities on the External 

 Surface of the Limbs 



The external covering, integument, or skin of the 

 horse is generally smooth, thick, and tough ; much 

 thicker on the back, flanks, and exposed portions of the 

 limbs, and thinner on the under and more protected parts. 

 Like the same structure in all other mammals, it is com- 

 posed of two very distinct parts : (1) An inner, thicker 

 layer, made up of interlacing filaments of tough, fibrous 

 tissue, to which blood-vessels and nerves are abundantly 

 distributed, and which also contain muscular fibres, and, 

 in its deeper portions, small collections of fatty tissue, 

 and everywhere numerous minute glands of two kinds, 

 sudoriferous and sebaceous, the former secreting a watery 

 fluid (the perspiration or sweat), and the latter an oily 

 substance which lubricates the skin and hair. This 

 layer is called the derm or corium. (2) Lying upon 

 this, and formed as an exudation or secretion of its 

 outer surface, is a layer called the epidermis, not sensi- 

 tive, and without blood-vessels, soft and moist in its 

 deeper and therefore newly-formed strata, and hard 

 and dry at its exposed surface. It is not fibrous, but 

 composed of cells which are at first nearly spherical 

 or polygonal, but gradually become flatter and more 

 scale-like as they approach the surface. Over the 

 greater part of the skin it forms an exceedingly thin 



