SEC. 8. THE MAMMARY GLAND. 



509. Since milk is a secretion, and indeed an excretion, the 

 mammary gland ought not to be classed as a metabolic tissue, in 

 the limited meaning we are now attaching to those words. Yet 

 the metabolic phenomena giving rise to the secretion of milk are 

 so marked and distinct, have so many analogies with the purely 

 metabolic events which take place in adipose tissue, and so 

 strikingly illustrate metabolic events in general, that it will be 

 more convenient to consider the matter here, rather than in any 

 other connection. 



The mammary gland, formed like a sweat gland, of which it 

 may be considered an extreme development, by an ingrowth of 

 the Malpighian layer of the epidermis, is a compound racemose 

 gland, constructed after the general plan of such a gland and thus 

 composed of branching ducts ending in secreting alveoli. 



The whole organ is divided by connective tissue septa into a 

 number of lobules, in woman about twenty, each of which possesses 

 a distinct duct, opening by a separate orifice on to the nipple ; the 

 gland in fact is not a single gland but several glands bound 

 together. Each lobe is further divided by connective tissue septa 

 into smaller lobes, and the division is repeated, the last divisions 

 marking out small masses called lobules. The main duct supplying 

 a lobe branches into a number of small ducts, each of the ultimate 

 divisions of which ends in a lobule. 



Within the lobule the duct divides into a number of 

 relatively wide tubules which pursue a wavy or even twisted 

 course, and bear deep lateral bulgings ; these are held together 

 by a comparatively slight amount of connective tissue. Hence 

 in a section of a gland, each lobule appears to be composed of 

 a number of irregularly round spaces or alveoli, which are the 

 sections of the tubules and the bulgings, and which at some parts 



