THE FEMALE REPRODUCTIVE ORGANS. 2 AI 



of the organ. During lactation the secreting tissue predominates, 

 and the septa are reduced to mere partitions ; before pregnancy 

 has taken place the connective tissue and fat form the bulk of the 

 organ, the glandular structures then being represented by the system 

 of ducts and excretory tubes, since the acini are present only as 

 small^ solid rudimentary cylindrical cell-masses. After lactation 

 the secreting parts of the organ atrophy and become much less con- 

 spicuous, some of the acini almost entirely disappearing, while con- 

 nective tissue and fat constitute the greater part of the mamma. 

 The termination of the period of sexual activity is followed by the 

 permanent atrophy of the gland-tissue, which finally is almost 

 complete, the entire mamma being then composed of connective 

 tissue and fat, with scarcely a trace of the former conspicuous se- 

 creting structures. The rudimentary breasts of children of both 

 sexes, and of the adult male, contain principally connective tissue, 

 in which excretory ducts, attached to small groups of immature 

 acini, lie embedded. Under exceptional circumstances the male 

 mammary gland may secrete true milk. 



The principal blood-vessels supplying the mammary glands run 

 mostly in the superficial tissues somewhat radially towards the areola ; 

 from these vessels on the anterior surface of the organ branches 

 penetrate into the glandular mass and pass between the lobules, 

 giving off twigs which break up into capillaries enclosing the alveoli. 

 The cutaneous papillae are supplied with capillary tufts where not 

 occupied by nervous structures. The vascular supply of the nipple, 

 while generous, does not include cavernous tissue, the erectility of 

 this part being due largely to the muscle. 



The lymphatics include the radicles enclosed within the fibrous 

 septa of the gland, as well as a net-work of subcutaneous lymph- 

 canals within the more superficial portions of the organ. The 

 lymphatic vessels are closely related to the surrounding chain of 

 lymphatic glands, as well as to those within the axilla. 



The nerves are distributed more richly to the superficial, cutaneous 

 parts of the organ than to its secreting tissue. They are principally 

 medullated fibres, those supplying the papillae of the nipple and the 

 areola in many cases ending in special tactile corpuscles ; the 

 nerves entering the base of the nipple often bear corpuscles of Vater. 

 The deeper parts of the glands receive principally the pale fibres 

 destined for the control of the blood-vessels, not, however, to the 

 exclusion of medullated fibres ; ganglion-cells have also been ob- 

 served in connection with the latter. 



Milk is composed microscopically of a clear fluid, the milk- 

 plasma, in which numbers of small oil-globules, 2-5 // in diam- 

 eter, together with the granular dbris of disintegrated cells, are 



16 



