1302 THE SKIN, MAMMARY GLANDS AND D UC TLESS GLANDS 



after the birth of the child. When their full functional activity is established, 

 their volume may be two or three times as great as before pregnancy. After lacta- 

 tion they return again nearly to their former size, which they retain until another 

 pregnancy. After the menopause the useless glands in some cases atrophy and 

 are reduced to small discoidal masses. In others, especially in fat individuals, 

 although the secreting tissue disappears, it is replaced by fat so that there is little 

 or no reduction in size. In addition to the above-mentioned variations in size, 

 the breasts are subject to great individual differences, the cause of which is little 

 understood. Large robust women are sometimes seen with small mammary 

 glands, and small women with large glands. In some individuals they are espe- 

 cially large. 



The weight of each mamma varies, naturally, with the volume, increasing from 30 to 60 

 centigrams in the small gland of a young child to 140 to 200 grams after pubertj^ and in nursing 

 women reaching 400 to 500 and occasionally 800 to 900 grams. 



The firm and elastic, well-developed breasts of young nulliparae become during lactation 

 even more firm and tense, but after lactation especially if there has been a long period of nursing 

 they lose their consistency and after several pregnancies become soft and flabby. 



The sulcus which defines the caudal border of the breast is but little marked in thin nulli- 

 parae, more marked in fat women, and especially evident in some multiparse. The relations of 

 the dorsal surface of the gland vary somewhat with the position. The level varies with the 

 stature; as a rule, in tall women it is more caudal and in short and broad-chested women it is 

 more cephalic. The tightness of the attachment to the sheath of the pectoralis major muscle is 

 quite variable, but even when quite loose there is some movement of the breast when the arm is 

 raised. The glandular tissue of that part of the breast which overhangs the axilla may be in 

 direct contact with the lymphatic glands. 



Structure. — The mammary glands are composed of the essential epithelial 

 glandular tissue, the parenchyma, the supporting and enclosing connective 

 tissue of the subcutaneous tela, the stroma, and the covering cutaneous layer. 



Parenchyma. — The essential part of each mamma is a flattened, circular mass 

 of glandular tissue of a whitish or reddish- white colour, the corpus mammae. This 

 is thickest opposite the nipple and thinner toward the periphery. The ventral 

 surface of this mass is convex and made uneven by numerous irregular pyramidal 

 processes which project toward the skin. The dorsal surface, or base, is flat or 

 slightly concave and much less irregular than the ventral surface. Minute proc- 

 esses of glandular tissue extend from the corpus mammae into the retromammary 

 tissue, some of them accompanying the septa of the pectoral fascia between the 

 bundles of muscle fibres of the pectoralis major muscle. The circumference of the 

 mamma is thick and well defined, more marked caudally than cephalically, but 

 it presents numerous irregular processes which extend beyond the limits apparent 

 from the surface. One of these especially large and well marked extends cephalo- 

 laterally into the axillary fossa, and there are frequently other large but less- 

 marked projections. 



The corpus mammae is not a single structure but is composed of from fifteen to 

 twenty separate lobes [lobi mammae] (fig. 1059). These are larger and smaller 

 irregular flattened pyramidal groups of glandular tissue, with their apices toward 

 the nipple and their bases radiating toward the periphery of the gland. 



Each lobe has a single excretory duct [ductus lactiferus] (figs. 1059, 1060, 

 1061), which opens by a contracted orifice [porus lactiferus] in a depression upon 

 the tip of the nipple. When traced from the pore toward the circumference of 

 the gland, the ducts are seen to run first directly dorsally through the nipple, 

 parallel and close to one another. From the base of the nipple they diverge. 

 Each duct is here visible to the unaided eye and measures from 1.5 to 2.5 mm. in 

 diameter. Beneath the areola its diameter increases for a short distance to from 

 4 to 9 mm., forming thus a reservoir, the ampulla or sinus lactiferus, in which the 

 secretion may accumulate for a time. Beyond this dilation the duct continues, 

 gradually decreasing in size as it breaks up into smaller and smaller branches, 

 There is no anastomosis between the ducts during their course, although at or 

 beneath the pore two or more ducts may join to have a common opening. They 

 possess no valves but when empty their inner surface is thrown into longitudinal 

 plicae. 



The ducts have an external coat of white fibrous connective tissue mixed with circular and 

 longitudinal elastic fibres. They are lined with a simple cuboidal or columnar epithelium, 

 except near < he orifice, where it is stratified squamous, l^lxfornal to the lining epitl)elium there 



