328 HAND-BOOK OF PHYSIOLOGY. 



exist among the various mucous membranes; and. the close relation be- 

 tween the secretion of the kidney and that of the skin is a subject of con- 

 stant observation. 



THE MAMMARY GLANDS AND THEIR SECRETION: MILK. 



Structure. The mammary glands are composed of large divisions or 

 lobes, and these are again divisible into lobules, the lobules being com- 

 posed of the convoluted subdivision of ducts (alveoli). The lobes and 

 lobules are bound together by areolar tissue; penetrating between the 

 lobes, and covering the general surface of the gland, with the exception 

 of the nipple, is a considerable quantity of yellow fat, itself lobulated by 



FIG. 221. Dissection of the lower half of the female mamma during the period of lactation. 

 %. In the left-hand side of the dissected part the glandular lobes are exposed and partially unrav- 

 eled; and on the right-hand side, the glandular substance has been removed to show the reticular 

 loculi of the connective-tissue in which the glandular lobules are placed: 1, upper part of the mainilla 

 or nipple; 2, areola; 3, subcutaneous masses of fat; 4, reticular loculi of the connective-tissue which 

 support the glandular substance and contain the fatty masses ; 5. one of three lactiferous ducts shown 

 passing toward the mamilla where they open; 6, one of the sinus lactei or reservoirs; 7, some of the 

 glandular lobules which have been unraveled; 7', others massed together. (Luschka.) 



sheaths and processes of tough areolar tissue (Fig. 221) connected both 

 with the skin in front and the gland behind; the same bond of connection 

 extending also from the under surface of the gland to the sheathing 

 connective tissue of the great pectoral muscle on which it lies. The main 

 ducts of the gland, fifteen to twenty in number, called the lactiferous or 

 galactophorous ducts, are formed by the union of the smaller (lobular) 

 ducts, and open by small separate orifices through the nipple. At the 

 points of junction of lobular ducts to form lactiferous difcts, and just be- 

 fore these enter the base of the nipple, the ducts are dilated (6, Fig. 221); 



