THE MAMMARY GLANDS 1303 



occurs in the smaller ducts a second layer of elongated cells resembling the myoepitheUum of the 

 sudoriparous glands. 



Each of the terminal branches of a duct ends in a tubulosaccular, spherical or pyriform alveo- 

 lus. A number of these alveoli which open into a common branch of the duct, when grouped 

 together and bound up with connective tissue, constitute a lobule of the gland (lobulus mammae). 

 A lobe is made up of all the lobules whose ducts join one common excretory duct. 



The alveoli are composed typically of a single layer of epithehal cells enclosed by a basement 

 membrane. This layer is the true secretory epithelium. It consists in the more active gland 

 of granular polyhedral or cuboidal cells which may be so closely placed as to leave almost no 

 lumen to the alveoU. During lactation these cells may be found in different stages of secretory 

 activity, their central ends being filled with minute oil globules and more or less flattened accord- 

 ing to the degree of distention of the alveoli. The alveoli and ductules now possess considerable 

 lumina which are filled with the above-mentioned milk globules hberated from the cells and sus- 

 pended in a serous fluid also secreted by the cells. This constitutes the milk (lac femininum). 



Stroma. — The lobes, lobules, and alveoU are completely covered by a connective-tissue 

 sheath too dehcate to constitute a distinct capsule. Outside of this the whole gland is embedded 

 in the subcutaneous tela which forms for it a sheath, capsula adiposa mammae. This is particu- 

 larly well developed on the ventral surface where the fat fills in between the irregularities caused 

 by the lobes and lobules and gives to the surface of the gland its smooth appearance. Within 

 the corpus mammae there is little fat between the lobules in nulliparte but much more fat is found 

 here in the stroma in multiparse. When the fat is absorbed, as it is during lactation and in 

 emaciation, the lobules stand out much more distinctly. There is however, no fat immediately 

 beneath the areola and nipple. The connective tissue is here loosely arranged and allows free 

 motility of the nipple and also permits the more easy distention of the ducts and sinuses during 

 lactation. The connective-tissue strands, retinacula mammae, which extend from the apices 

 of the glandular processes on the ventral surface of the mamma are connected to the corium and 

 correspond to the retinacula cutis found in other situations. These are sometimes particularly 

 well developed over the cephalic part of the mamma and have been called the suspensory liga- 

 ment of Cooper. 



The dorsal surface of the mamma is bound to the pectoral fascia b}'^ loose connective tissue 

 containing, as a rule, only a small amount of retromammary fat (figs. 1060, 1061). The attach- 

 ment to the sheath of the pectoralis major muscle is at times so loose that the spaces between 

 the connective tissue appear to form serous sinuses, the sub- or retromammary bursae. 



In addition to the axillary process or 'tail' of the gland, a projection is sometimes seen extend- 

 ing toward the sternum and another caudolaterally; also processes extending toward the clavicle 

 and caudomedially have been described. Besides these large projections there are numerous 

 branched interlacing processes which combine into larger and smaller masses on the ventral 

 surface and exist as minute extensions on the dorsal surface. In thin women, the parenchyma 

 at the apex of these triangular processes reaches nearly to the surface. 



A mammary gland may be made up of a larger amount of stroma and a smaller amount of 

 glandular tissue, or the reverse, and therefore a small breast may furnish more milk than a large 

 one. There is also a variation in different parts of the same breast, one lobe or section may have 

 well-developed lobules while in another they remain almost as at puberty, merely branching 

 ducts. 



The glandular tissue when sectioned is whitish with a greyish or pinkish cast and is firm and 

 resistant, almost cartilaginous in consistency. It is thus easily distinguished from the adipose 

 capsule. 



Changes due to age and functional activity. — At birth the mamma consists mainly of 

 fifteen to twenty slightly branched ducts lined with stratified squamous or columnar epithelium. 

 In spite of the lack of true glandular tissue, within the first few days there may be such rapid 

 cell proliferation that the ducts become distended with cells and detritus. By pressure upon the 

 gland a few drops of this material may be expressed which constitutes the so-called 'witches 

 milk.' From birth until puberty the mamma remains rudimentary, simply keeping pace with 

 the general body growth, but in the female, at puberty, an abrupt change occurs. The tubules 

 grow rapidly into the surrounding tissue and some acini (alveoli) appear; the stroma and fat are 

 also greatly increased; and the breast becomes rounded and well formed but consists mainly of 

 fatty stroma and ducts, with but a very small number (if any) of true secreting acini. At this 

 time in both boys and girls the breast may become swollen and tender and a milk-hke seci'etion 

 may be produced similar to that at birth. The great increase in volume during pregnancy and 

 lactation is due to the increase in the size and number of the lobules and acini, and is accom- 

 panied by a decrease in the interlobular and intralobular stroma and in the fat, so that the gland 

 feels hard and uneven. The acini appear first in the periphery, thence along the larger ducts 

 toward the centre of the corpus mammaj. 



The secretion of the gland for the first two or three days after parturition until the free secre- 

 tion of milk is estabhshed is termed the colostrum. It differs from normal milk not only in 

 chemical composition but also in containing larger fat globules and special cells known as 

 colostrum corpuscles. 



The decrease of the gland nearly to its original size after lactation is due to an involution 

 of the parenchyma, the acini being reduced to narrow tubules, most of them completely atrophy- 

 ing. With this is associated a development of fat and fibrous stroma. The gland does not, 

 however, regain its virgin appearance but its main mass is looser and more irregular, less dis- 

 tinct, and the peripheral processes larger, while the stroma contains numerous fat -lobules. This 

 causes the breast to be less smooth, firm, and elastic, and it tends to become pendulous and form 

 a sulcus where it overhangs its base. With the end of sexual activity the secreting portions of 

 the glands gradually atrophy, finally leaving httle more than the ducts. Even these undergo 

 senile atrophy, and the main mass of the gland is represented onl}^ by a flattened disc, in which 

 the peripheral processes can scarcely be made out. In fat women there may be httle reduction 

 in size, but the breast is here transformed almost entirely into fat. 



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