MAMMARY GLANDS. 75 



branches, composed of fibrous tissue and lined with colum- 

 nar 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 male the glands are from one half an inch to two inches 

 broad, and from ^ to J of an inch in thickness. In their 

 structure, however, they present 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 different 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 ramifications, which have 

 gradually been developed as processes from the main duct. 

 It is important to remember, however, that these branches 

 are never so numerous nor so long during the intervals of 

 lactation as they are when the organ is in full activity. 

 The ordinary condition of the gland, as compared with its 

 structure during activity, is that of atrophy. 



Condition of the Mammary Glands during the Intervals 

 of Lactation. At this time the gland is not a secreting 

 organ. It presents the ducts, ramifying, to a certain extent, 

 in the substance of the lobes into which the structure is di- 

 vided, but their branches are short and possess but few of 

 the glandular acini that are observed in every part of the 

 organ during lactation. This difference in the structure 

 of the gland is most remarkable; and as it passes from 

 a secreting to a non-secreting condition at the end of lacta- 

 tion, 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 ap- 

 pearance which it presents during activity. The ducts are 

 then lined with a small, nucleated, pavement-epithelium, 

 which is not found during the secretion of milk. These 

 changes, pointed out by Robin, whose observations have 



