544 



THE REPRODUCTIVE SYSTEM 



epithelium rests upon a reticular or homogeneous basement mem- 

 brane, within which are occasional basket cells. These have been in- 

 terpreted as smooth muscle cells, similar to those of the secretory por- 

 tions of the sweat glands. 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 fibers. 



The ducts of the mammary gland are lined by either a single or 

 double row of low columnar cells. They possess a relatively broad lumen. 

 Their membrana propria is supported by a thin connective tissue wall, 



PUfc * 





FIG. 476. ACTIVE MAMMARY GLAND OF RABBIT (22 DAYS AFTER FECUNDATION.) 

 The alveoli are filled with milk containing fat droplets. X416. (After L. Schil.) 



The alveoli are filled with a stainable milk coagulum in which are many fat spher- 

 ules. 



containing both circular and longitudinal elastic fibers but no muscle. 

 The elastic fibers of the smaller ducts are poorly developed, but in suit- 

 able specimens the longitudinal fibers are readily seen even in very 

 small branches. Beyond the lactiferous sinus the duct epithelium 

 changes to a stratified squamous variety which is continuous with that 

 of the cutaneous surface of the nipple. 



The glandular lobules are firmly united by strong septa derived from 

 the dense areolar tissue in which they are embedded. In the deeper 

 parts of the gland occasional lobules of fat are found in this tissue. 

 Within the nipple and beneath the adjacent portions of the areola, smooth 



