PHYSIOLOGICAL ANATOMY OF THE MAMMARY GLANDS. 365 



fully developed, and, if examined with the microscope, they are found to lack the essential 

 anatomical characters of secreting organs. The physiological anatomy of the mammary 

 glands consequently possesses peculiar interest, aside from the great importance of their 

 secretion. 



It will be found convenient to consider these organs in three stages of development; 

 viz., in their rudimentary condition, as they exist in the male and in the female before 

 puberty ; in the partially-developed state, as they are found in the unimpregnated female 

 after puberty and during the intervals of lactation; and, finally, in the fully-developed 

 condition, when milk is secreted. 



Physiological Anatomy of the Mammary Glands. 



The form, size, and situation of the mammae in the adult female are too well known 

 to demand more than a passing mention. These organs are almost invariably double 

 and are situated on the anterior portion of the thorax, over the great pectoral mus- 

 cles. In women who have never borne children, they are generally firm, nearly hemi- 

 spherical, with the nipple at the most prominent point. In women who have borne 

 children, the glands, during the intervals of lactation, are usually larger, are held more 

 loosely to the subjacent parts, and are apt to become flabby and pendulous. The areola 

 of the nipple is also darker. 



In both sexes, the mammary glands are nearly as fully developed at birth as at any 

 time before puberty. They make their appearance at about the fourth month, in the 

 form of little elevations of the structure of the true skin, which soon begin to send off 

 processes beneath the skin, which are destined to be developed into the lobes of the 

 glands. In the foetus at term, the glands measure hardly more than one-third of an inch 

 in diameter. At this time, there are from twelve to fifteen lobes in each gland, and 

 each lobe is penetrated by a duct, with but few branches, composed of fibrous tissue 

 and lined with columnar epithelium. The ends of these ducts are frequently somewhat 

 dilated ; but what have been called the gland- vesicles do not make their appearance 

 before puberty. In the adult male, the glands are from half an inch to two inches 

 broad, and from -^ to of an inch in thickness. In their structure, however, they pre- 

 sent little if any difference from the rudimentary glands of the infant. 



As the period of puberty approaches in the female, the rudimentary ducts of the differ- 

 ent lobes become more and more ramified. Instead of each duct having but two or three 

 branches, the different lobes, as the gland enlarges, are penetrated by innumerable rami- 

 fications, which have gradually been developed as processes from the main duct. It is 

 important to remember, however, that these branches are never so numerous or so long 

 during the intervals of lactation as they are when the organ is in full activity. The ordina- 

 ry condition of the gland, as compared with its structure during activity, is one of atrophy. 



Condition of the Mammary Glands during the Intervals of Lactation. At this 

 time the glands are not secreting organs. They present the ducts, ramifying, to a certain 

 extent, in the substance of the lobes into which the structure is divided, but their branches 

 are short and possess but few of the glandular acini that are observed in every part of 

 the organs during lactation. This difference in the structure of the glands is most 

 remarkable ; and, as they pass from a secreting to a non-secreting condition at the end of 

 lactation, the ducts retract in all their branches, and most of the secreting culs-de-sac 

 disappear. At this time, the glandular tissue is of a bluish-white color and loses the 

 granular appearance which it presents during functional activity. The ducts are then 

 lined with a small, nucleated, pavement-epithelium, which is not found during the secre- 

 tion of milk. These changes, pointed out by Robin, whose observations have been veri- 

 fied and extended by Sappey, are confined almost exclusively to the secreting structure of 

 the glands. The interstitial tissue remains about the same, the blood-vessels, only, being 

 increased in number during lactation. 



