46 DISEASES OF THE HORSE’S Foot 
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 papille. These 
project into the epidermis, which is moulded on them. 
For the most part the papilla 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 
