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Henry Gray (1825–1861).  Anatomy of the Human Body.  1918.
 
 
3d. 6. The Mammæ
 
  
(Mammary Gland; Breasts)


The mammæ secrete the milk, and are accessory glands of the generative system. They exist in the male as well as in the female; but in the former only in the rudimentary state, unless their growth is excited by peculiar circumstances. In the female they are two large hemispherical eminences lying within the superficial fascia and situated on the front and sides of the chest; each extends from the second rib above to the sixth rib below, and from the side of the sternum to near the midaxillary line. Their weight and dimensions differ at different periods of life, and in different individuals. Before puberty they are of small size, but enlarge as the generative organs become more completely developed. They increase during pregnancy and especially after delivery, and become atrophied in old age. The left mamma is generally a little larger than the right. The deep surface of each is nearly circular, flattened, or slightly concave, and has its long diameter directed upward and lateralward toward the axilla; it is separated from the fascia covering the Pectoralis major, Serratus anterior, and Obliquus externus abdominis by loose connective tissue. The subcutaneous surface of the mamma is convex, and presents, just below the center, a small conical prominence, the papilla.
  The Mammary Papilla or Nipple (papilla mammæ) is a cylindrical or conical eminence situated about the level of the fourth intercostal space. It is capable of undergoing a sort of erection from mechanical excitement, a change mainly due to the contraction of its muscular fibers. It is of a pink or brownish hue, its surface wrinkled and provided with secondary papillæ; and it is perforated by from fifteen to twenty orifices, the apertures of the lactiferous ducts. The base of the mammary papilla is surrounded by an areola. In the virgin the areola is of a delicate rosy hue; about the second month after impregnation it enlarges and acquires a darker tinge, and as pregnancy advances it may assume a dark brown or even black color. This color diminishes as soon as lactation is over, but is never entirely lost throughout life. These changes in the color of the areola are of importance in forming a conclusion in a case of suspected first pregnancy. Near the base of the papilla, and upon the surface of the areola, are numerous large sebaceous glands, the areolar glands, which become much enlarged during lactation, and present the appearance of small tubercles beneath the skin. These glands secrete a peculiar fatty substance, which serves as a protection to the integument of the papilla during the act of sucking. The mammary papilla consists of numerous vessels, intermixed with plain muscular fibers, which are principally arranged in a circular manner around the base: some few fibers radiating from base to apex.

Development.—The mamma is developed partly from mesoderm and partly from ectoderm—its bloodvessels and connective tissue being derived from the former, its cellular elements from the latter. Its first rudiment is seen about the third month, in the form of a number of small inward projections of the ectoderm, which invade the mesoderm; from these, secondary tracts of cellular elements radiate and subsequently give rise to the epithelium of the glandular follicles and ducts. The development of the follicles, however, remains imperfect, except in the parous female.

Structure (Figs. 1172, 1173).—The mamma consists of gland tissue; of fibrous tissue, connecting its lobes; and of fatty tissue in the intervals between the lobes. The gland tissue, when freed from fibrous tissue and fat, is of a pale reddish color, firm in texture, flattened from before backward and thicker in the center than at the circumference. The subcutaneous surface of the mamma presents numerous irregular processes which project toward the skin and are joined to it by bands of connective tissue. It consists of numerous lobes, and these are composed of lobules, connected together by areolar tissue, bloodvessels, and ducts. The smallest lobules consist of a cluster of rounded alveoli, which open into the smallest branches of the lactiferous ducts; these ducts unite to form larger ducts, and these end in a single canal, corresponding with one of the chief subdivisions of the gland. The number of excretory ducts varies from fifteen

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