176 THE STEUCTUEE OF THE HOESE. 



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 pro- 

 tected parts. Like the same structure in all other 

 mammals, it is composed 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 fibers, and, in its deeper 

 portions, small collections of fatty tissue, and every- 

 where numerous minute glands of two kinds, sudor- 

 iferous 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 coriiim. (2) Lying 

 upon this, and formed as an exudation or secretion 

 of its outer surface, is a layer called the epidermis, 

 not sensitive, 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 be- 

 come flatter and more scale-like as they approach the 



