THE MAMMARY GLANDS 



439 



history may repeatedly pass through the cycle of secretory changes, 

 though the exact number of such cycles which an individual cell 

 may present obviously does not admit of demonstration. 



As a rule, the active epithelium consists of a single row of cells, 

 though here and there they appear as if piled upon one another 



b I 



FIG. 353. FROM THE ACTIVELY SECRETING MAMMARY GLAND OF A WOMAN. 



Several lobules are included, a, interlobular duct ; 6, iuterlobular connective tissue. 



Hematein and eosin. Photo, x 52. 



to form a double layer. The epithelium rests upon a reticular or 

 homogeneous basement membrane, within which are occasional 

 basket cells (Korbzellen). The alveoli of the active gland are so 

 closely packed that a connective tissue tunica propria is no more 

 than scarcely demonstrable. The thin tunica propria is, however, 

 richly supplied with blood capillaries, lymphatic vessels, and nerve 

 fibres. 



