1304 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS 



The skin covering the ventral surface of the breast is very white, covered with 

 lanugo hairs associated with sebaceous glands, and contains many sweat glands of 

 the ordinary type. It is so thin that the subjacent veins are readily seen through 

 it. It is closely adherent to the subjacent fatty laj'^er but its flexibility, elasticity, 

 and motility over the deeper glandular tissue permit much stretching during the 

 enlargement which occurs at the time of lactation. In spite of this, linea albi- 

 cantes are often produced especially when the breasts have been unusually large. 

 Aside from the above-mentioned particulars it does not differ from the skin of 

 the adjacent part of the thorax, except over the centre of the breast where it 

 forms the areola and nipple. 



The areola mammae (figs. 1058, 1059, 1060, 1061) is covered by a thin, deli- 

 cate, pigmented skin. The colour in young nulliparae is reddish, the shade varying 

 with the complexion. During pregnancy the colour darkens, slightly in blondes, 

 but so as to become almost black in marked brunettes. 



This pigmentation serves as one of the signs of gestation. After lactation the colour fades, 

 but little pigmentation remaining in blondes, considerable in brunettes. During pregnancy- 

 there is sometimes seen extending more or less beyond the areola a less deeply and less uniformly 

 pigmented ring, the secondary areola. In size, the areola is subject to considerable individual 

 variation and is increased in pregnancy. 



The surface of the areola is roughened by a number of slight elevations irregu- 

 larly arranged. These are due to underlying large sebaceous and rudimentary 

 milk glands [gl. areolares; Montgomerii], tubercles of Montgomery. Projections 

 caused by sebaceous glands are also found in the secondary areola. All of these 

 tubercles enlarge greatly during pregnancy and the glands produce a slight secre- 

 tion which is discharged through ducts that open on their summits. The sweat 

 glands are few but large, and in addition to the lanugo hairs there are usually 

 several well-developed hairs. 



The corinm of the areola is devoid of fat but contains a well-developed layer of smooth muscle 

 fibres, the fascicles of which intercross in various directions but may be seen to be mainly of two 

 orders, circular and radial. They are continuous with those of the nipple. The circular 

 fibres are most numerous adjacent to the nipple, where they may form a layer nearly 2 mm. in 

 thickness. 



The areola varies greatly in size, measuring from 15 to 60 mm. in diameter. There is some 

 confusion in regard to the areolar glands and the tubercles of Montgomery. Some consider 

 the tubercles to be caused by the areolar glands, others consider them caused by the sebaceous 

 glands. Sebaceous glands undoubtedly cause the projections in the secondary areola. The 

 sudoriferous glands of the areola are large and compound tubular glands with a compUcated 

 glomerulus and are considered as transitions between sweat and mammary glands. The seba- 

 ceous glands are even more numerous than the sudoriferous and are composed of several lobes. 

 They also have been considered by some as intermediate stages in the formation of mammary 

 glands, but this is improbable. There are ten to fifteen very small areolar glands (though Pinard 

 found an average of but four to each breast), whose structure is essentially identical with that 

 of the principal mammary glands. They have dilations on their ducts and they open on the 

 areola at times in common with a sebaceous gland. 



The nipple [papilla mammae] (figs. 1058, 1059, 1060, 1061) in well-developed 

 nulliparae is situated slightly meso-caudal to the centre of the breast and on a 

 level with the fourth rib or fourth intercostal space about 12 cm. from the median 

 line. But its position in reference to the thoracic wall varies greatly with age, 

 individual, and the present and past activity of the gland. The nipple is usually 

 somewhat conical or cylindrical with a rounded fissured tip marked by fifteen to 

 twenty minute depressions into which the lactiferous ducts empty. The average 

 length of the nipple is 10 mm. to 12 mm. The skin is thin, wrinkled, and pig- 

 mented like the areola, except over the tip of the nipple where there is no pigment. 



The corium of the nipple has many large vascular and nervous papilhc and there is no fat in 

 it. Hair.s and sudoriffMous glands are absent but sebaceous glands are present in great numbers. 

 Their .secnition here and over the areola serves to keep tlic skin soft and to protect it from the 

 saliva of the nursing infant. In tlio dcM^por layers of the corium smootli muscle fibres form a 

 loose stratum continuous with that of the areola. This is made u]) principally of an external 

 circular layer and to a slight extent by an iiitcrnallaycr whose bundles of fibres are parallel with 

 the milk ducts. Numerous interlacing niuKcIc fil)n's connected with these layers and mixed 

 with loose connective tissue, and elastic fibres, but no fat, surround the lactiferous ducts as they 

 pass through the axis of the nipple. 



I'ho nipple usually does not project from the surface luitil the third year. It soon becomes 

 conical but docs not attain its full size until shortly aff(n- puberty. The size of the nipple is 

 variable, ordinarily in proi)ortion to the size of the gland, but large nipples arc sometimes found 

 on small breasts and small nipples on large breasts. During pregnancy the nipple increases in 



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