46 DISEASES OF THE HORSE'S rOOT 



is a series of flattened, granular-looking cells known as the 

 stratum granulosum. 



Immediately above the stratum granulosum the horny 

 portion of the epidermis commences. In the human skin 

 this is formed of three distinct layers. Undermost a layer 

 of clear compressed cells, the stratum lucidum. Next above 

 it a layer of swollen cells, the nuclei of which are indis- 

 tinguishable. Finally, a surface layer of thin, horny scales, 

 the stratum squamosum, which become detached and thrown 

 off in the form of scurf or dandruff. In the skin of the 

 horse, except where it is thickest, these layers are not 

 clearly defined. 



It is the Malpighian layer of the epidermis that is most 

 active in cell division. As they are formed the new cells 

 push upwards those already there, and the latter in their 

 progress to the surface undergo a chemical change in which 

 their protoplasm is converted into horny material. This 

 change, as we have already indicated, takes place above 

 the stratum granulosum. 



In addition to its constant formation of cells to replace 

 those cast off from the surface, the active proliferation of 

 the elements of the Malpighian layer is responsible for the 

 development of the various appendages of the skin, the 

 hairs with their sebaceous glands, the sweat glands, horny 

 growths and the hoof, and, in the human subject, the 

 nail. These occur as thickenings and down-growths of the 

 epithelium into the corium. 



The epidermis is devoid of bloodvessels, but is provided 

 with fine nerve fibrils which ramify between the cells of 

 the rete mucosum. 



The Corium is composed of dense connective tissue, the 

 superficial layer of which bears minute papillae. These 

 project into the epidermis, which is moulded on them. 

 For the most part the papillae contain looped capillary 

 vessels, rendering the superficial layer of the corium 

 extremely vascular. Why this must be a moment's reflec- 

 tion will show. The epidermis, as we have already said* 

 is devoid of bloodvessels. It therefore depends entirely 



