THE MAMMARY GLANDS 1305 



size and becomes more sensitive and more easilj' erectile. The shape of the nipple in addition to 

 conical or cylindrical may be hemispherical, flattened, discoidal, or shghtly pedunculated. Its 

 end may be invaginated or the entire nipple retracted beneath the surface of the gland and pro- 

 jecting only in response to stimuli. 



The circular muscle fibres of the nipple act like those at its base in the areola. By inter- 

 mittent, rhythmic contractions they tend to empty the lactiferous ducts; by continuous and tight 

 contraction they act as a sphincter. When contracted they also narrow the nipple, make it 

 harder, erect, and more projecting. When the vertical fibres contract they depress the tip of 

 the nipple or they may retract the whole nipple beneath the surface. The muscle of the areola 

 when stimulated puckers the skin toward the nipple causing circular concentric folds in the 

 skin of the areola. 



The male mammary gland [mamma virilis]. This develops exactly as with 

 the female. From birth to puberty the glands in the two sexes have a parallel 

 growth and development, but from this time on the glands in the male grow but 

 slightly and reach their full development about the twentieth year. 



The corpus mammae in the adult male measures from 1.5 to 2.5 cm. in diameter and .3 to 

 .5 cm. in thickness. It is whitish in colour, tough, and stringy. It is composed of the same 

 number of lobes as in the female but these consist of little more than short ducts with no true 

 acini and may be reduced to mere epithelial or connective-tissue strands. The areola and nipple 

 are present and pigmented, but the nipple averages only 2 to 5 mm. in height. The areola has 

 a diameter of 2 to 3 cm. and is covered with hairs. The areolar tubercles may be recognised 

 and the areolar muscle is present. The position of the nipple in relation to the chest-wall is 

 more constant than in the female as the breast is less movable. It is seldom beyond the limits 

 of the fourth intercostal space or the two adjacent ribs, and averages 12 cm. from the median 

 line. Occasionally the male breast may hj-pertrophy on one or both sides, gynecomastia. 



Blood-supply. — The main arterial supply to the mammary gland is from mam- 

 mary rami of perforating branches of the internal mammary artery (p. 567). 

 Usually that from the second or third intercostal space is especially large. Small 

 branches, external mammary rami, are also supplied to the caudal and lateral 

 segments of the breast by the lateral thoracic artery (p. 571 ). Some rami from 

 the thoracoacromial or supreme thoracic arteries (p. 571) may reach the cephalo- 

 lateral segment of the breast and small twigs, lateral mammary rami, from the 

 anterior branches of the lateral cutaneous rami of the aortic intercostal arteries (p. 

 589) supply its deep surface. 



These vessels anastomose freely and form a wide- meshed network in the stroma of the ventral 

 and dorsal surfaces from which branches proceed around the lobes and lobules and finally form a 

 close network of capillaries around the alveoli. From these, venous capillaries arise and pass in 

 two groups, one deep, accompanying the arteries, the others superficial. These latter extend to 

 the ventral surface of the gland to form a loose network beneath the skin. During lactation 

 these subcutaneous veins show through the skin as bluish lines, and frequently form a more or 

 less complete circle around the nipple. They connect with the superficial veins of the neck 

 superiorly, with those of the abdomen inferiorly, and with the thoracoepigastric vein laterallj-. 

 The deep veins carry the blood to larger vessels, which empty into the subclavian, the inter- 

 costal, the internal mammary, and the axillary; and the superficial group may connect with the 

 external jugular and femoral veins. 



The lymphatics. — The lymphatics of the mammse are extremely numerous, 

 forming rich plexuses and free anastomoses. Their exact origin and distribution 

 are not yet fully understood, but it is clear that there is a rich plexus in the skin of 

 the areola and nipple which empties mainly into a subareolar plexus. Deep lym- 

 phatics arise in the spaces around the alveoli in all parts of the gland, and most of 

 these converge toward the nipple where they join the subareolar plexuses. Thej^ 

 anastomose freely with the cutaneous lymphatics and many of them emptj' into 

 the subareolar plexus through large lymph-vessels which run parallel with the 

 lacteal ducts. From the subareolar plexus usually two large Ij-mph-vessels arise 

 and pass toward the axilla to empt}^ into the axillary lymph-glands (p. 719). 

 Other lymphatic vessels of the mammary gland follow the course of the various 

 blood-vessels. 



There is usually a third trunk from the cephalic part of the breast and often a fourth from 

 the caudal segment which join with the others to the axillary glands. The lymphatics of the 

 mammary gland also communicate with the lymphatics of the skin, the ventral chest-wall 

 and those of the deep fascia over the pectoral muscles, as well as the lymphatics of the opposite 

 side. They also empty into the lymphatics which accompany the blood-vessels of this region, 

 and thus commimicate with the axillary, subclavicular, and supraclavicular Ij-mphatic nodes 

 (p. 722). Moreover, those from the medial portion of the gland accompany the branches of 

 the internal mammary artery and empty into the sternal glands along the artery within the 

 thorax. Since cancer of the breast extends and is disseminated through lymphatic channels, 

 their distribution and connections are of great practical importance. 



