S86 THE SENSE ORGANS AND SKIN OF THE HORSE 
THE APPENDAGES OF THE SKIN 
The appendages of the skin are modifications of the epidermis, and comprise 
the hairs, hoofs, claws, horns, ete. 
The hairs (Pili) cover almost the entire surface of the body in the domesticated 
mammals, and some parts which appear at first sight to be bare are found on close 
inspection to be provided with sparse and very fine hair. The hairs are constantly 
being shed and replaced, but at certain periods in the horse, for example, they fall 
out in great numbers, constituting the shedding of the coat. It is customary to 
distinguish the ordinary hairs (the coat), which determine the color of the animal, 
from the special varieties found in certain places. Among the latter are the long 
Fic. 709.—Latrerat View or Horse to SHow HatR-STREAMS AND Vortices. (After Ellenberger-Baum, Anat. fir 
Kiinstler.) 
tactile hairs about the lips, nostrils, and eyes; the eyelashes or cilia; the tragi of 
the external ear; and the vibrisse of the nostrils. Other special features will be 
noted in the discussion of the skin of the various species. The hairs are directed 
in such a way as to form more or less definite hair-streams (Ilumina pilorum), 
and at certain points these converge to form vortices (Vortices pilorum). 
The part of the hair above the surface of the skin is the shaft (Scapus pili), 
while the root (Radix pili) is embedded in a depression termed the hair-follicle 
(Folliculus pili). A vascular papilla (Papilla pili) projects up in the fundus of the 
follicle and is capped by the expanded end of the root, the bulb of the hair (Bulbus 
pili). The hair-follicles extend obliquely into the corium to a varying depth; im 
the case of the long tactile hairs they reach to the underlying muscle. Most of the 
follicles have attached to them small unstriped muscles known as the arrectores 
pilorum; these are attached at an acute angle to the under side of the deep part 
