The fresh hide consists of two layers : an outer, the epidermis; and an inner, the true akin. The epidermis is very thin as compared with the true akin which it covers, and is entirely removed preparatory to tanning ; it nevertheless possesses important functions. It is shown in Fig. 893 at a, and more highly magnified in Fig. 894. Its inner mucous layer b, the rete which rests upon the true skin c, is soft, and composed of living cells, which are elongated in the deeper layers, and gradually become flattened as they approach the surface, where they dry up, and form the horny layer a. This last is being constantly worn away, and thrown off as dead scales of skin ; and as constantly renewed from below, by the continued multiplication of the cells. It is from this epithelial layer that the hair, as well as the sweat- and fat-glands, are developed. It will be seen in Fig. 893 that each hair is surrounded by a sheath, which is continuous with the epidermis. In em bryonic development, a small knob of cells forms on the under side of the epidermis, and this en larges, and sinks deeper into the true skin, while the root of the young hair is formed within it. Smaller projections also form on the stalk of the knob, and in due time produce the sebaceous glands ; this is shown in Fig. 895, a b. The pro cess of development of the sudoriferous glands is very similar to that of the hairs. There is a great analogy between this pro cess and that of the or dinary renewal of hair in the adult animal. At d', Fig. 893, is seen an old and worn-out hair. It is shrunken and elongated, and is almost ready to fall out. It will be noticed that its sheath or follicle projects somewhat below the hair to stage of the right. This is the first production of u young hair, and is quite analogous to the knob of epithelium which has been described as forming the starting point of a hair in the embryo. At d", the same process is seen further advanced, the young hair being already formed, and growing up into the old sheath. At d"', it is complete, the old hair having fallen out, and the young one having taken its place.
The hair itself is covered with a layer of overlapping scales, like the slates on a roof, but of irregular form. These give it a serrated outline at the sides, strongly developed in wool. Within these scales, which are sometimes called the " hair cuticle," is a fibrous substance, which forms the body of the hair ; and sometimes, but not always, there is also a central and cellular pith, which is mostly transparent, though under the microscope it frequently appears black and opaque, from the optical effect of imprisoned air. On boiling or long soaking in water, alcohol, or turpentine, these air-spaces become saturated with the liquid, and then appear transparent.
The fibrous part of the hair is made up of long spindle-shaped cells, and contains the pigment which gives the hair its colour. The hair of the deer differs from that of most other animals in being wholly formed of polygonal cells, which, in white hairs, are usually filled with air. At its base, the hair swells into a bulb, which is hollow, and rests on a sort of projecting knob of tho 001414771 called the hair-papilla. This has blood-vessels and nerves, and supplies nourishment to the hair. The hair-bulb is composed of round, soft cells, which multiply rapidly ; as they grow, they press upward through the hair-sheath, become elongated and hardened, and form the hair. In dark hairs, both tho cells of the hair itself and those of its follicle or sheath are strongly pigmented, hut the hair much the more so, and hence the bulb has usually a distinct dark form. The dark-hairod portions of a hide from which the hair has been removed by liming still
remain coloured, from the pigmented cells of the hair-sheaths, which can only be got out by bating and scudding. The cells outside the bulb shown at f, in Fig. 896, pass upwards as they grow, and form a distinct coating around the hair, which is called the "inner root-sheath." This again consists of two separate layers, of which the inner is "Huxley's," the outer, "Henle's." They arise from the same cells in the base of the hair; but in the inner layer, these remain polygonal and nucleated, while in the outer, they become spindle-shaped and without nuclei. The inner root-sheath does not extend to the surface of the skin, but dies away below the sebaceous glands. This figure represents an ox hair root, mag. 200 dia. : a, fibrous suhstance of hair ; 1, hair cuticle ; e, inner root-sheath ; d, outer root-sheath ; e, dermic coat of hair sheath ; f, origiu of inner sheath ; g, bulb ; h, papilla.
Outside the inner root-sheath is a layer of nucleated cells, con tinuous with those of the epidermis, and of the same character. This is the "outer root-sheath," and is shown at d, Fig. 896. This, together with the whole of the epidermis, is covered next the corium with an exceedingly fine membrane, called the " hyaline " or glassy layer. The whole of the hair-sheath is enclosed in a coating of elastic and connective-tissue fibres, which are supplied with nerves and blood vessels, and form part of the corium. Near the opening of the hair sheaths to the surface of the skin, the ducts of the sebaceous or fat-glands (e, Fig. 893), pass into them, and secrete a sort of oil to lubricate the hair. The glands themselves are formed of large nucle ated cells, arranged somewhat like a bunch of grapes ; one is shown highly magnified in Fig. 897: a, sebaceous gland ; 1, hair-stem ; e, part of erector pill muscle. The upper and more central cells are most highly•charged with fat, which is shown by the darker shading.
As already remarked, the sudoriferous or sweat-glands are also derived from the epidermis layer. They are shown at f, Fig. 893, and on a larger scale (200 dia.) in Fig. 898: a, windings laid open in making section ; they consist, in the ox and sheep, of a large wide tube, sometimes slightly twisted. In this, they differ considerably from those of man, which form a spherical knot of extremely convoluted tube. The walls of these glands are formed of longitudinal fibres of connective tissue of the corium, lined with a single layer of large nucleated cells, which secrete the perspiration. The ducts, which are exceedingly narrow, and with walls of nucleated cells like those of the outer hair-sheaths, sometimes open directly through the epidermis, as shown at g, but more frequently into the orifice of a hair-sheath, just at the surface of the skin. Each hair is provided with a slanting muscle (h, Fig. 893), called the arrector or erector pili, which is contracted by cold or fear, and causes the hair to " bristle," or stand on end ; by forcing up the attached skin, it produces the effeot known as " goose-skin." The muscle, which is of the unstriped or involuntary kind, passes from near the hair-bulb to the epidermis, and just under the sebaceous glands, which it compresses.