Outside the inner root-sheath is a layer of nucleated cells, continuous with those of the epidermis, and of the same character. This is the "outer root-sheath," and is shown at _d_, Fig. 4. This, together with the whole of the epidermis, is covered next the _corium_ with an exceedingly fine membrane, called the "hyaline" or glassy layer. It is possible that this forms the very thin buff-coloured "grain" of tanned leather, which evidently is of different structure from the rest of the _corium_, since, if it gets scraped off before tanning, the exposed portion of the _pars papillaris_ remains nearly white, instead of colouring. 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. 1), pass into them, and secrete a sort of oil to lubricate the hair. The glands themselves are formed of large nucleated cells, arranged somewhat like a bunch of grapes; one is shown highly magnified in Fig. 5: _a_, sebaceous gland; _b_, hair-stem; _c_, part of _erector pili_ muscle. The upper and more central cells are most highly charged with fat, which is shown by the darker shading. [Illustration: Fig. 5.] As already remarked, the sudoriferous or sweat-glands are also derived from the epidermis layer. They are shown at _f_, Fig. 1, and on a larger scale (200 diam.) in Fig. 6: _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_, Fig. 1, 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. 1), 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 effect 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. [Illustration: Fig. 6.]