2028 



HUMAN ANATOMY. 



and separate glands, opening by independent ducts, that collectively constitute the 

 true secreting organ (corpus mammae), as distinguished from the enveloping layer of 

 fat and areolar tissue. 



As seen. in the young, well-developed subject, before the occurrence of preg- 

 nancy, the mammae form two hemispherical projections that lie upon the thoracic 

 wall, one on either side of the sternum, extending from the outer margin of the latter 

 to the axillary border and from the level of the second to that of the sixth rib. The 

 outline of the organ is not quite circular but elliptical, the horizontal diameter, from 

 IO-I2 cm. (4-4^ in.), being about one centimetre more than the vertical. The 

 height of the projection measures about 5.5 cm. The rounded contour of the breast 

 depends chiefly upon the fat that forms a complete envelope for the glandular tissue, 



Fig. 1 710. 



■^■**= 



Areola 



Areolar 

 glands 



Nipple 



Ampulla 

 Lactiferous duct 

 Left mamma drawn frotr living subject ; ducts and glandular tissue have been drawn from dissection. 



except beneath the nipple and, in places, on the deep muscular surface. In the young 

 subject, in whom the gland has never enlarged in consequence of pregnancy, the secre- 

 tory tissue is relatively small in amount and masked by the fat that penetrates between 

 the lobules. The approximate summit of each breast, when firm and non-pendulous 

 as in young women, is marked by the conical or wart-like nipple (papilla mammae), 

 which lies opposite the lower border of the fourth rib and is pierced by the excretory 

 canals, or lactiferous ducts, from the lobes. The nipple, about i cm. high, and 

 marked by numerous shallow furrows, is surrounded by the areola, a cutaneous zone 

 about 4. 5 cm. in diameter that is modelled by minute low elevations produced by the 

 small subcutaneous areolar glands, or glands of Montgomery, which represent isolated 

 accessory portions of secretory tissue. Although varying with the complexion, the 



