THE FURTHER DEVELOPMENT OF THE FEMALE MAMMARY GLAND AND ITS RETROGRESSION IN OLD AGE.
Up to the time of puberty the growth of the gland bears a close rela tion to the bodily growth in both sexes; only a few gland-lobules are developed by proliferation. According to Hennig the right areola is always better formed than the left.
With the onset of puberty, there is a further development of the gland in females. Up to this time the excretory ducts are but slightly formed, being for the most part blind sacs; now true terminal vesicles are formed, although of a more bulbous shape.
Soon the connective tissue which immediately surrounds these gland ducts has a peculiar compact hyaline quality; it is especially rich in nuclei, and different from the bundles of connective tissue which lie between the lobules; this peculiar covering of connective has doubtless an important relation not only to the later richer growth of vessels, but also to the development of the so frequently present pseudo-plasma in the mammary glands.
Later the terminal vesicles develop into regular grape-like acini. These acini contain small round cells, such as epithelium; the excre tory ducts have cylindrical epithelium. Coincidently the size of the gland increases, the epithelium grows by proliferation, while capillaries and firm connective tissue surround the newly developed acini. The acini and ex cretory ducts contain no secretion; the firm elastic consistency of the virgin breast is due to the peculiarly firm quality of its connective tissue.
During the first pregnancy, the number of acini greatly increases, especially by the development of the parietal acini; the lobules become larger, and the underlying cellular tissue becomes richer in vessels and more succulent. Whilst in a virgin breast the single lobules cannot be separated from the connective tissue, and the developed breast which does not contain milk appears to the naked eye as thick, firm connective tissue, when the organ contains its secretion the single gland-masses are easily apparent in the surrounding connective tissue.
The appearance of lobules filled with milk is shown in Fig. 5.
More highly magnified, the acini present the appearances seen in Figs. 6, A and 6, B.
In the functionating organ not only is every acinus distended with milk, but the surrounding connective tissue is very much richer in cell elements, which appear larger and more succulent, which is not the case in the non-secreting organ. By this enlargement and rich development of capillary vessels and lymphatics, the mamma assumes an appearance similar to that of other acinous glands, as the salivary and lachrymal glands. I have not been able to find a separate investing membrane of the acini, though it has been mentioned by many authors. According to Langer each acinus is sharply defined by a fine nucleated fibrous net-work. This highly developed condition is that in which the gland is most fre quently described. The developed nipple is very contractile; it contains a large number of muscular fibres, which belong only to the cutis not to the excretory ducts, and the muscular fibres of the skin in this region are gen erally strengthened. According to Hennig, these muscular fibres extend also deep into the gland, so that they surround, in interrupted layers, not only the excretory ducts but also the single gland-lobules.
The nipple is pierced by from twelve to fifteen excretory ducts, which are here so small that the finest bristle can scarcely penetrate them. The small, previously-mentioned nodules of the areola, which, with the areola, are of a brown or brownish-black color during pregnancy, are small acin ous glands and are considered by most authors as sebaceous glands of the skin. Luschka believes that these so-called Montgomery's glands, as shown by Duval, are important parts of the milk-glands (glanduks lae tiferce aberrantes), which do not perforate the nipple, but end in the areola. Either view is sound if we regard all the lacteal glands as sebaceous glands. Hennig thinks that sexual intercourse, without resulting pregnancy, has more to do with the develop ment of Montgomery's glands than with the size of the areola and the weight of the glands.