1002 THE MAMMARY GLANDS. 



MAMMARY GLANDS. 



The mammary glands (mammae), the organs of lactation in the female, 

 are accessory parts to the reproductive system. They give a name to a 

 large class of animals (Mammalia), which are distinguished by the possession 

 of these organs. When fully developed in the human female, they form, 

 together with the integuments and a considerable quantity of fat, two 

 rounded eminences (the breasts) placed one at each side on the front of the 

 thorax. These extend from the third to the sixth or seventh rib, and from 

 the side of the sternum to the axilla. A little below the centre of each 

 breast, on a level with the fourth rib, projects a small conical body named the 

 nipple (mammilla), which points somewhat outwards and upwards. The sur- 

 face of the nipple is dark, and around it there is a coloured circle or areola, 

 within which the skin is also of a darker tinge than elsewhere. In the 

 virgin, these parts are of a rosy pink colour, but they are always darker in 

 women who have borne children. Even in the second mouth of pregnancy, 

 the areola begins to enlarge and acquire a darker tinge ; these changes go 

 on increasing as gestation advances, and are regarded as reliable sigus in 

 judging of suspected pregnancy. After lactation is over, the dark colour 

 subsides, but not entirely. The skin of the nipple is marked with many 

 wrinkles, and is covered with papillae ; besides this, it is perforated at the 

 tip by numerous foramina, which are the openings of the lactiferous ducts : 

 and near its base, as well as upon the surface of the areola, there are scat- 

 tered rounded elevations, which are caused by the presence of little glands 

 with branched ducts, four or five of which open on each elevation. The 

 tissue of the nipple contains a large number of vessels, together with much 

 plain muscular tissue, and its papillae are highly sensitive ; it is capable of 

 a certain degree of erection from mechanical excitement, which may be 

 partly caused by turgescence of its vessels, but is probably due, in greater 

 part, to contraction of the muscular fibres. 



The base of the mammary gland, which is nearly circular, is flattened, 

 or slightly concave, and has its longest diameter directed upwards and 

 outwards towards the axilla. It rests on the pectoral muscle, and is con- 

 nected to it by a layer of areolar tissue. The thickest part of the gland 

 is near the centre, opposite the nipple, but the full and even form of the 

 breasts depends chiefly on the presence of a large quantity of fat, which 

 lies beneath the skin, covers the substance of the gland, and penetrates the 

 intervals between its lobes and lobules. This fatty tissue, which is of a 

 bright yellow tinge and rather firm, is divided into lobulated masses by 

 numerous laminae of fibrous or very dense areolar tissue, which are con- 

 nected with the skin on the one hand, and on the other with the firm 

 areolar investment of the gland itself, which investment is connected behind 

 by similar laminae with the areolar membrane covering the pectoral muscle ; 

 these laminae serve to support the gland. Beneath the areola and the 

 nipple there is no fat, but merely the firm areolar tissue and vessels sur- 

 rounding the lactiferous ducts. 



Structure. The mammary gland consists of a number of distinct 

 glandular masses or lobes, each having a separate excretory duct, held 

 together by a very firm intervening fibrous or areolar tissue, and having 

 some adipose tissue penetrating between them. Each of these divisions of 

 the gland is again subdivided into smaller lobes, and these again into 

 smaller and smaller lobules, which are flattened or depressed, and held 

 together by areolar tissue, blood-vessels, and ducts. The substance of the 



