ANATOMY OF THE BREASTS.
They form soft hemispherical projections above the surface of the body, and extend, when well-developed, vertically from the third to the seventh rib, and horizontally from the edge of the sternum to the anterior border of the axillary space; being situated for the most part on the pectoralis major muscle, and to a less degree on the serratus magnus (Luschka). It is worthy of note that these glands, at the same period of life and under similar functional conditions, differ in size, not only in different women, but also in the same individuals, and that there is no fixed relation between their size and that of the body. The circumference of the gland depends not only upon the amount of the gland-substance, but to a great degree upon the amount of the superimposed adipose tissue. Very near the middle of each gland is situated the nipple, in which the excretory ducts empty, and around which the skin is of a light rose-red or brown color for a distance of 1 inches. According to Hennig the mammary gland has frequently a three-cornered shape, and one can distinguish an inner and two outer (an upper and a lower) extremities; the upper external extremity not infrequently sends out a process which extends under the pectoralis major muscle nearly to the axillary glands. The nipple does not generally denote the central point of the denuded gland, but is some what internal to and above it. The right mammary gland is usually somewhat larger and heavier than the left.
The mammary glands belong to the class of aggregate acinose glands, and are to be considered in their whole development ancisituation as seba ceous glands of the skin, whose function is to secrete a fat emulsion (milk). As is well-known, this function is by no means a constant one, but depends upon certain occurrences in the sexual organs. In this respect there are analogous processes in the other sebaceous glands, in that the fluidity, the softness and amount of the secretion of these glands stand in a certain re lation to the sexual organs, and that upon this relationship depends the great softness of the female skin.
Between the mammary glands of a newly-born child and those of a pregnant woman, there exist such great ,qualitative and quantitative dif ferences, that an especial consideration of these glands under these differ ent circumstances is necessary, especially since a knowledge of these differences is of great weight in order to properly understand the patho logical processes.
The arteries of the mammary glands are chiefly given off from the in ternal mammary and long thoracic arteries; the branches of these arteries anastomose to a considerable extent, and are much enlarged during the activity of the gland. They spread out into finer and finer twigs, until they form a capillary net-work surrounding the single lobules. From ihese capillary net-works arise numerous venules, which, following the course of the arteries, form dense net-works under the skin, and finally empty into the internal mammary and thoracic vein; many of the sub cutaneous veins emptying into the external jugular (Luschka).
The mammary glands are very rich in lymphatic plexuses, which are partly situated deep down in the gland, partly subcutaneous. They form tolerably narrow closed plexuses, not communicating with the connective tissue interspaces (Langhaus), which surround the lobules of the glands near the capillary plexuses and accompany the excretory duct. They arise from club-like processes in the papillae of the mammary areola (as in the skin), form cutaneous and subcutaneous plexuses, and then unite to form lymphatic trunks. The superficial as well as the deep lymphatic trunks pass for the most part to the lymphatic glands of the axillary space, where they unite with the lymphatic vessels of the intercostal spaces and through these with those of the thoracic cavity. (Luschka).
The nerves of the mammary glands are mostly of spinal origin, though to some extent there is a mixture of sympathetic elements. There are, according to Eckhart, especially, branches from the 4 to 6 intercostal nerves, which accompany the larger milk-ducts and are distributed in the parenchyma of the gland. Their mode of termination is not yet known, though it is very probable that they end in terminal bulbs, as they do in other acinose glands (as in the salivary glands, W. Krause). The skin over the mammary glands is very rich in nerves, which come from the internal and middle supraclavicular nerves, and from the external branches of the 2 to 6 intercostal nerves (Luschka).