THE MAMMARY GLANDS. 



2029 



FIG. 1711. 



Suspensory band 



Pectoral muscle 



pigmentation of the integument covering the nipple and areola is very slight, and 

 hence the color of these parts is usually a rosy pink. After the earlier months of 

 pregnancy the color of the nipple and areola changes to brown, in varying shades of 

 intensity, which tint thereafter never entirely disappears, but becomes temporarily 

 augmented with each pregnancy. 



The mammary gland lies within the superficial fascia of the thorax, which not 

 only forms a general investment for the or- 

 gan, but also sends into it septa that mate- 

 rially aid in supporting the fat and glandular 

 tissue. Local peripheral thickenings of the 

 fascia occur above and below and assume the 

 character of suspensory bands, those above 

 being known as the ligaments of Cooper. 

 Although for the most part separated from 

 the underlying muscle by a layer of fascia that 

 permits of shifting of the mamma, its deepest 

 lobules may occupy recesses between the fas- 

 ciculi of the pectoralis major. 



Structure. The corpus mammae con- 

 sists of from 15-20 or more flattened pyrami- 

 dal lobes (lobi mammae), each of which is a 

 distinct gland measuring from 1.52 cm. The 

 lobes are radially disposed, the groups of al- 

 veoli or lobules lying towards the periphery 

 and the excretory ducts converging towards 

 the nipple, upon which they open. When 

 enlarged, as during lactation, the lobes pro- 

 duce irregularities in the outline and on the 

 surface of the gland-mass that may be felt 

 through the covering of adipose tissue. Each 

 lobe is subdivided by connective tissue into 

 several lobules (lobuli mammae), which in turn 

 are made up of the ultimate divisions of the 

 secreting tissue or alveoli. The latter are 

 sacular compartments, the walls of which con- 

 sist of a well-defined membrana propria, or 

 basement membrane, lined, in the resting con- 

 dition, by a double layer of cells. Those 

 next the membrana propria are probably to 

 be regarded as muscular in nature (Lacroix, 

 Benda), thus emphasizing the resemblance 

 between the mammary and sweat glands. 



The inner cells, the secretory elements, are cuboid or low columnar, from .005- 

 .007 mm. high, and present the usual appearances of glandular epithelium. 



During lactation the alveoli become greatly enlarged and distended and the 

 intervening connective tissue correspondingly reduced, so that the alveoli are pressed 

 closely together, the general appearance of the tissue often recalling that of the 

 lung. Under such conditions the secreting cells vary with the distention of the 

 alveoli, being low in large compartments and higher in those less expanded. The 

 protoplasm of the cells actively engaged in the production of milk contains minute 

 oil droplets that occupy chiefly the inner zone. As these increase in size, they press 

 the nucleus towards the basement membrane and project into the alveolus, being 

 separated from the lumen by only a thin protoplasmic stratum. Finally, the latter 

 ruptures, and the oil droplets escape into the albuminous fluid that is additionally 

 secreted by the glands and occupy the alveolus. After liberation of the oil droplets, 

 the epithelial cell is much reduced in height, but after a time again becomes the 

 seat of renewed accumulation of fat and the production of milk-globules. Destruc- 

 tion of the fat-liberating cells, therefore, does not take place. 



The excretory ducts begin as the minute canals into which the alveoli open. 



Gland- 

 tissue 



Fascial envelope 



Sagittal section of mamma of young woman who had 

 never borne children ; hardened in formalin. 



