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The follicles of these hairs extend down into the derma, and from the upper end of the follicle, i.e. near the aperture of the invagination, a long cellular outgrowth extends down into the derma, branches at its end, and becomes hollow. These branches are the tubules of the future milk gland. Another outgrowth from the follicle forms a sebaceous gland.
This is clear evidence that the milk gland was evolved in connexion with hairs, and was an enlargement of glands opening into the hair follicle, but it is difficult to understand why a sebaceous gland is developed and afterwards disappears.
Thus a granulating surface may be covered entirely by the ingrowing of the cutaneous epithelium from the margins; or islets, originating in surviving cells of sebaceous glands or sweat glands, or of hair follicles, may spring up in the centre of the raw area. Such islets may also be due to the accidental transference of loose epithelial cells from the edges.
It is probable that the decomposition of the contents is the result of the presence of bacteria, and that from the surgical point of view they should be regarded as infective. A sebaceous cyst may remain indefinitely without change, or may slowly increase in size, the skin over it becoming stretched and closely adherent to the cyst wall as a result of friction and pressure.
Dermoid cysts of the ovary may consist only of a wall of connective tissue lined with epidermis and containing distinctly epidermic scales which, however, may be rolled up in firm masses of a more or less soapy consistency; this variety is called by Orth epidermoid cyst; or, according to Warren, a form of cyst made up of skin containing small and ill-defined papillae, but rich in hair follicles and sebaceous glands.
This is a cancer originating in the sweat glands or sebaceous follicles, or in the fœtal residues of cutaneous glands. The cells are small and closely packed together in alveoli or in reticulated columns; cell nests are rare. It is rare on the trunk or limbs. It commences as a small flattened nodule in the skin, the epidermis over it being stretched and shining.
All over the surface of the body are to be found innumerable little sebaceous glands originally intended to lubricate hairs, which have now atrophied and disappeared. These useless scraps, under various forms of irritation, both external and internal, become inflamed and give rise to pimples, acne, or "a bad complexion." And so the list might be drawn out to most impressive length.
Deformities of the nose causing enormous development, or the condition called "double-nose" by Bartholinus, Borellus, Bidault, and others, are ordinarily results of a pathologic development of the sebaceous glands. In some cases tumors develop from the root of the nose, forming what appears to be a second nose. In other cases monstrous vegetations divide the nose into many tumors.
We have the odoriferous glands of sebaceous origin, and with them the prepuce of the clitoris which has been described as a kind of gigantic sebaceous follicle with the clitoris occupying its interior.
Later on the hairs and the sebaceous glands entirely disappear, and the milk gland alone is left with its tubules and ducts opening into the cavity of the teat.
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