THE SKIN OF THE HOESE — 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 caudae). 



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 bursas (Bursas subcutaneae) may be present at various prominent 

 points, e. g., the olecranon, the tuber coxae, the tuber calcis, the withers, etc. 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 ungulae) 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 posteriorly at an acute angle to form the bars. The latter (Pars 

 inflexa medialis, lateralis)^ appear on the ground surface of the hoof as convergent 



' The term foot is used here in the popular sense, i. e., to designate the hoof and the structures 

 enclosed within it. 



2 The term "pila ungulae" has been suggested by Schmaltz for the part popularly known as 

 the "bar." 



