THE SKIN OF THE HORSE—THE HOOF 887 
of the follicle, and their contraction causes erection of the hair and compression of 
the sebaceous glands, one or more of which open into the follicle. 
The hairs are composed of epidermal cells, and consist from without inward of 
three parts. The cuticle is composed of horny, scale-like cells which overlap like 
slates on a roof. The cortex consists of horny fusiform cells which are packed close 
together and contain pigment. The medulla is the central core of softer, cubical 
or polyhedral cells; it contains some pigment and air-spaces. 
The hair-follicles, being invaginations of the skin, are composed of a central 
epidermal part and a peripheral layer which corresponds in structure to the corium. 
The follicles of the tactile hairs have remarkably thick walls which contain blood- 
sinuses between their outer and inner layers; in ungulates the sinuses are crossed 
by trabeculse and assume the character of cavernous or erectile tissue. 
The hoofs, claws, horns, and other horny structures consist of closely packed 
epidermal cells which have undergone cornification. In structure they might be 
compared to hairs matted together by intervening epidermal cells. They cover a 
specialized corium from which the stratum germinativum derives its nutrition. 
THE SKIN OF THE HORSE 
The thickness of the skin of the horse varies from one to five millimeters in 
different regions, and is greatest at the attachment of the mane and on the tail. 
The glands are numerous and are larger than those of the other domesticated 
animals. The sebaceous glands are specially developed on the lips, the prepuce, 
mammary glands, perineum, and labia of the vulva. The sweat glands are yellow 
or brown in color. They occur in almost all parts of the skin, but are largest and 
most numerous in that of the lateral wing of the nostril, the flank, mammary glands, 
and free part of the penis. 
In addition to the ordinary and tactile hairs certain regions present coarse 
hairs of great length. The mane (Juba) springs from the dorsal border of the neck 
and the adjacent part of the withers; its anterior part, which covers the forehead 
to a variable extent, is termed the foretop (Cirrus capitis). The tail, with the 
exception of its ventral surface, bears very large and long hairs (Cirrus caudz). 
The tuft of long hairs on the flexion surface of the fetlock (Cirrus pedis) gave rise to 
the popular name of this region. 
The development of these special hairs varies widely, and is in general much greater in the 
draft breeds than in others. In Shire and Clydesdale horses, for instance, the hair on the poste- 
rior aspect of the metacarpus and metatarsus and fetlock is often so long and abundant as to ac- 
count for the term “‘feather,’’ which is commonly applied to it by horsemen. 
Subcutaneous burse (Burs subcutanex) may be present at various prominent 
points, e. g., the olecranon, the tuber cox, the tuber calcis, the withers, ete. They 
are not present in the young subject and appear to be the result of traumatism. 
THE HOOF 
The hoof (Ungula) is the horny covering of the distal end of the digit. It is 
convenient to divide it for description into three parts, termed the wall, sole, and 
frog. 
1. The wall (Paries ungule) is defined as the part of the hoof which is visible 
when the foot is placed on the ground.! It covers the front and sides of the foot, 
and is reflected posterioriy at an acute angle to form the bars. The latter (Pars 
inflexa medialis, lateralis)? appear on the ground surface of the hoof as convergent 
1 The term foot is used here in the popular sense, 7. e., to designate the hoof and the structures 
enclosed within it. 
a ey term “pila ungule” has been suggested by Schmaltz for the part popularly known as 
e o ar.” 
