. A text-book of embryology for students of medicine [electronic resource]. Embryology; Embryology. THE MAMMARY GLAND. 275 the second month. At this time the deep layer of the epidermis, in the sites of the future glands, becomes thick- ened by the multiplication of its cells, the thickened patch encroaching upon the underlying corium (Fig. 136, A, b). This thickened area enlarges somewhat peripherally and its margins become elevated, owing to which latter circumstance the patch appears relatively depressed (B). The depression is known as the glandular area, and it corresponds with the future
. A text-book of embryology for students of medicine [electronic resource]. Embryology; Embryology. THE MAMMARY GLAND. 275 the second month. At this time the deep layer of the epidermis, in the sites of the future glands, becomes thick- ened by the multiplication of its cells, the thickened patch encroaching upon the underlying corium (Fig. 136, A, b). This thickened area enlarges somewhat peripherally and its margins become elevated, owing to which latter circumstance the patch appears relatively depressed (B). The depression is known as the glandular area, and it corresponds with the future areola and nipple. In many mammals the develop- ment of the milk-glands is initiated by the appearance of a. Fig. 136.—Sections representing three successive stages of development of the human mamma (Tourneux): A, fetus of mm. ( in.); B, of cm. (4 in.); C, of cm. ( in.); a, epidermis; b, aggregation of epidermal cells forming anlage of gland; c, galactophorous ducts; d, groove limiting glandular area; e, great pectoral muscle; /, unstriated muscular tissue of areola; g, subcutaneous adipose tissue. pair of linear thickenings of the epidermis on the ventro- lateral aspect of the body, called the milk-ridges or milk- lines, from localized thickenings of which the multiple mammary glands of such animals develop. These milk- lines have also been observed in the human embryo, but the constancy of their occurrence in man lias not as yet been established. From the bottom of the glandular area, numerous small masses or bud-like processes of cells grow down into the corium. Some of the buds acquire lateral branches. By the hollowing out of these cell-buds the latter are transformed. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Heisler, John Clement; Waterstone, David, former owner; Duke-E
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