460 DISEASES OF THE HORSE. 
The fibrous bundles of the true skin contain plain, muscular fibers, 
which are not controlled by the will, but contract under the influence 
of cold and under certain nervous influences, as in some skin dis- 
eases and in the chill of a fever, and lead to contraction, tightening, 
or corrugation of the skin, contributing to produce the “ hidebound ” 
‘of the horseman. Other minute, muscular filaments are extended 
from the surface of the dermis to the hair follicle on the side to which 
the hair is inclined, and under the same stimulating influences pro- 
duce that erection of the hair which is familiarly known as “ staring 
coat.” Besides these, the horse’s skin is furnished with an expansion 
of red, voluntary muscle, firmly attached to the fibrous bundles, and 
by which the animal can not only dislodge insects and other irritants, 
but even shake off the harness. This fleshy envelope covers the sides 
of the trunk and the lower portions of the neck and head, the parts 
unprotected by the mane and tail, and serves to throw the skin of 
these parts into puckers, or ridges, in certain irritating skin diseases. 
The hairs are cuticular products growing from an enlarged papilla 
lodged in the depth of a follicle or sac, hollowed out in the skin and 
extending to its deepest layers. The hair follicle is lined by cells of 
epidermis, which at the bottom are reflected on the papilla and be- 
come the root of the hair. The hair itself is formed of the same kind 
of cells firmly adherent to one another by a tough, intercellular sub- 
stance, and overlapping each other, like slates on a roof, in a direc- 
tion toward the free end. 
The sebaceous glands are branching tubes ending in follicles or 
sacs and opening into the hair follicles, lined by a very vascular 
fibrous network representing the dermis, and an internal layer of 
cells representing the mucous layer of the cuticle. The oily secretion 
gives gloss to the hair and prevents its becoming dry and brittle, and 
keeps the skin soft and supple, protecting it at once against undue 
exhalation of water and undue absorption when immersed in that 
medium. Besides those connected with the hair follicles there are 
numerous, isolated, sebaceous glands, opening directly on the sur- 
face of the skin, producing a somewhat thicker and more odorous 
secretion. They are found in large numbers in the folds of the skin, 
where chafing would be liable if the surface were dry, as on the 
sheath, scrotum, mammary glands, and inner side of the thigh, around 
the anus and vulva, in the hollow of the heel, beneath the fine horn 
of the frog, on the inner side of the elbow, on the lips, nostrils, and 
eyelids. When closed by dried secretion or otherwise these glands 
may become distended so as to form various-sized swellings on the 
skin, and when inflamed they may throw out offensive, liquid dis- 
charges, as in “grease,” or produce red, tender. fungous growths 
(“‘ grapes.”) 
