366 SECRETION. 



Structure of the Mammary Glands during Lactation. Between the fourth and the 

 fifth month of utero-gestation, the mammary glands begin to increase in size ; and, at 

 term, they are very much larger than during the unimpregnated state. At this time, the 

 breasts become quite hard, and the surface near the areola is somewhat uneven, from 

 the great development of the ducts. The nipple itself is increased in size, the papillae 

 upon its surface and upon the areola are more largely developed, and the areola becomes 

 larger, darker, and thicker. The glandular structure of the breasts during the latter half 

 of pregnancy becomes so far developed, that, if the child be born at the seventh month, 

 the lacteal secretion may generally be established at the usual time after parturition. 

 Even when parturition takes place at term, a few days elapse before secretion is fully 

 established, and the first product of the glands, called colostrum, is very different from the 

 fully-formed milk. 



The only parts of the covering of the breasts that present any peculiarities are the 

 areola and the nipple. The surface of the nipple is covered with papillaa, which are 

 very largely developed near the summit. It is covered by epithelium in several layers, 

 the lower strata being filled with pigmentary granules. The true skin covering the nip- 

 ples is composed of inelastic and elastic fibres, containing a large number of sebaceous 

 glands, but no hair-follicles or sudoriparous glands. According to Sappey, these glands, 

 which are from eighty to one hundred and fifty in number, are always of the racemose 

 variety, and they never exist in the form of simple follicles, as they are described by most 

 anatomists. The nipple contains the lactiferous ducts, fibres of inelastic and elastic tis- 

 sue, with an immense number of non-striated muscular fibres. The muscular fibres have 

 no definite direction, but are so numerous that, when they are contracted, the nipple 

 becomes very firm and hard. The nipple, although it may thus become hard upon the 

 application of cold or other stimulus, presents none of the anatomical characteristics of 

 the true erectile organs, as is erroneously supposed by some authors ; and its hardening 

 is simply due to contraction of its muscular fibres. 



The areola does not lie, like the general integument covering the gland, upon a bed 

 of adipose tissue, but it is closely adherent to the subjacent glandular structure. The 

 skin here is much thinner and more delicate than in other parts, and the pigmentary 

 granules are very abundant in some of the lower strata of epidermic cells, particularly 

 during pregnancy. The true skin of the areola is composed of inelastic and elastic fibres 

 and lies upon a distinct layer of non-striated muscular fibres. The arrangement of the 

 muscular fibres (sometimes called the subareolar muscle) is quite regular, forming con- 

 centric rings around the nipple. These fibres are supposed to be useful in compressing 

 the ducts during the discharge of milk. The areolar presents the following structures : 

 numerous papilla, considerably smaller than those upon the nipple ; hair-follicles, con- 

 taining small, rudimentary hairs ; sudoriparous glands ; and sebaceous glands connected 

 with the hair- follicles. The sebaceous glands in this situation are very large, and their 

 situation is indicated by little prominences on the surface of the areola, which are espe- 

 cially marked during pregnancy. 



The mammary gland itself is of the compound racemose variety. It is covered in 

 front by a subcutaneous layer of fat, and posteriorly it is enveloped in a fibrous membrane 

 loosely attached to the pectoralis major muscle. A considerable amount of adipose tissue 

 is also found in the substance of the gland between the lobes. 



Separated from the adipose and fibrous tissue, the mammary gland is found divided 

 into lobes, from fifteen to twenty-four in number. These, in their turn, are subdivided 

 into lobules made up of a greater or less number of acini, or culs-de-sac. The secreting 

 structure is of a reddish-yellow color and is distinctly granular, presenting a decided 

 contrast to the pale and uniformly fibrous appearance of the gland during the intervals 

 of lactation. If the ducts be injected from the nipple and be followed into the substance 

 of the gland, each one will be found distributing its branches to a distinct lobe ; so that 

 the organ is really made up of a number of glands, in their structure identical with each 



