904 THE SENSORY APPARATUSES. 



In Solipeds and other animals, the epidermis is generally dark-coloured, from 

 the presence of pigment-corpuscles, the number of which increases with their 

 depth in the membrane. This coloration is perhaps intended to prevent the 

 rubefacient effects of the heat of the sun's rays, by augmenting the absorbing 

 and dispersing power of the cutaneous surface. In the majority of cases, this 

 coloration is absent in the Sheep, whose skin is protected by a thick fleece ; and 

 also in tlie Pig, whose habits in a wild, as in a domesticated condition, keep it 

 out of the direct action of the sun. 



(In some regions of the body of all animals, the skin forms folds, as at the 

 junction of the fore limb with the body, the flank, and between the thighs. In 

 the Cow, it forms the large pendulous layer at the throat and breast, known as 

 the " dewlap ; " and in the Goat and Pig, it not unf requently constitutes teat- 

 like prolongations depending from the throat, which nearly always contain a 

 small cartilaginous nucleuc and some muscular fasciculi. The thickness of the 

 epidermis is sometimes greatly increased by wear and friction, as we frequently 

 see in the skin covering the knees of Sheep, etc.) 



(The functions of the skin are, as we have seen, tactile and secretory ; m 

 addition, it is eminently protective. Its secretory action is always more or less 

 active, but the production of perspiration is greatest when the body is at a high 

 temperature, as during active exertion ; at other times the perspiration is 

 insensible. In this respect, the skin has intimate sympathetic relations with 

 other organs which have somewhat analogous functions, such as the lungs, 

 kidneys, intestines, etc., and when its function is disordered or checked, it 

 induces alterations in the secretions of one or all of these organs. The skin is 

 also the seat of a constant and important respiratory action, as it absorbs oxygen 

 and throws off carbonic acid, and any interruption to this process is injurious.) 



The skill of Ruminants shows, at certain points, depressions destitute of hair, but extremely 

 rich in sebaceous glands. Such is the tear fossa situated on the face, and tl biflex canal 

 between the digits— as in the Sheep, and particularly in the Goat. (It should be remarked 

 that sioeat-glanih are found in the skin of the Ox, and in tl. ; pads of the feet of Dogs and Cats. 

 They attain a great size in the pig's snout. The nos; and upper lip of Ruminants, and that of 

 the Dog an<i Cat, contain racemose glands that secrete : clear, watery, alkaline fluid.) 



Article II.— Appendages of the Skin. 



Preparation. — See treatises on histology. 



The appendages of the skin are hairs and horny productions^ dependencies of 

 the epidermic layer. 



Hairs. 



The hairs are the filaments which, collectively, form the external covering of 

 the skins of animals. 



In the Horse, the bristly appendages known as horsehair should be dis- 

 tinguished from the hairs proper ; the latter are fine and short — particularly 

 in the regions where the skin is thin — imbricated on each other, and spread 

 over the entire surface of the body in c continuous layer which is designated 

 the coat. The former are long and flowing, occupy the summit of the head, 

 where they constitute the forelock ; the upper border of the neck, where they 

 form the mane ; and cover the caudal appendage with a splendid tuft — the tail. 

 Some of these also form special organs on the free margin of the eyelids, and 

 are termed eyelashes ; while others, inserted about the lips and below the eyes, 

 are named tentacula. (The eyelashes are chiefly implanted in the upper lid. 



