APPENDAGES OF THE SKIN 



133 



of the body the feet, for example which are subject to constant attrition. 

 In the horse there are first and most important the hoofs, which protect 

 the internal foot, the oval-shaped bodies on the inside of the fore-legs 

 immediately above the knee-joint, and the inside of the hind-legs, just 

 balow the hock, described as chestnuts, and the bodies which have already 

 been mentioned behind the fetlock-joints, the ergots. A careful exami- 

 nation of all these horny productions will prove that in their elementary 

 structure they are composed of the same elements as the hair which covers 

 the animal body. They rest upon, and are 

 secreted by, a papillated membrane, and consist 

 entirely of cells varying in form and character 

 much the same as they do in the several parts 

 of the hair, from the centre to the surface. The 

 horn fibres or hairs passing from the coronet to 

 the ground surface, forming the crust, and the horn fibres passing from 

 the vascular membrane at the bottom of the foot to the ground, forming 

 the sole, may all be resolved into epithelial cells, like those of the cuticle. 

 Altogether, the structure of horn may be said to consist of bundles of 

 hair closely applied to each other to form a compact covering to the parts 



* 



Fig. 262. Lamella; of Horn 



Fig. 263. Transverse Section of Horn 



Fig. 264. Longitudinal Section of Horn 



beneath. In certain diseases, " canker" of the feet, for example, the horn 

 on the diseased surface always appears in the form of tufts of hair, or 

 of horn fibres, which, in consequence of the disease, have failed to adhere 

 and form a compact structure. The study of the anatomy of the hair 

 of different animals, as compared with the horny production, is an exceed- 

 ingly interesting one, and it is perfectly easy to find the analogues in 

 the hairs of some of the thick-skinned animals, such as the rhinoceros 

 and the elephant, transverse sections of which, when examined by the 

 microscope, can hardly be distinguished from transverse sections of the 

 hoof of the horse. 



