INTEGUMENT OF MAMMALS 



145 



secretion liberated at the base of the eyelash. Somewhat similar 

 ceruminons glands lining the external auditory meatus s(>orete a 

 waxy su})stance. ]\Iost mammals have mucus-])rodncing and lubri- 

 cating epidermal glands associated with the skin of the external 

 reproductive structures. In the skin near the anus of some forms 

 there are modified sebaceous glands producing odoriferous secre- 

 tions. 



Mammary Glands. These glands, which are for the most part 

 located in the dermis, arise from invaginations of the embryonic 

 skin. They form in both male and female, but normally develop 

 to functional maturity only in the female and undergo regressive 



Fig. 87. — Mammary gland of human in intermediate stage of activity, showing 

 two lobules with an interlobular duct breaking into two mtralobular ducts that 

 extend into the secreting end-pieces. A dense connective tissue surrounds the 

 lobules and groups them into lobes. 



changes in the male. Each mammary gland (Fig. 87) is compound 

 aheolar in form. The excretory ducts open in the nipple, which is 

 a conical extension of connective tissue covered with epidermis. 

 The alveolar portions of the mammary glands are large and com- 

 posed of pyramidal cells, but there is considerable ^•ariation in size 

 depending on the secretory state of the gland. When acti^'e, fat 

 globules accumulate in the cytoplasm toward the free end of the cells 

 and the enlarged terminal portions are discharged into the lumen. 

 The remaining nucleated basal portion of each cell soon repeats the 

 process. Secretions accumulating in the lumen pass along small 

 ducts which open into the larger lactiferous ducts. The number 

 10 



