34 INTRODUCTION TO SEXUAL PHYSIOLOGY 



alveoli are lined with short cohnnnar cells from which the con- 

 stituents of the milk (fat, lactose, proteins, etc.) are poured 

 out without the cells breaking down in the process. In this 

 respect, therefore, the mammary glands resemble the salivary 

 glands ratlier than the sebaceous glands, in which latter there 

 is actual cell disintegration in the process of secretion. 



Fio. 22. — Section of maniniary gland (human) during lactation 

 (highly magnitied). a, Alveoli ; 6, duct. 



The smaller or lobular ducts unite to form the lactiferous 

 ducts, which are fifteen to twenty in number, and open by separate 

 apertures on the nipple. Where the lobular and lactiferous 

 ducts join there are dilatations which form reservoirs for the milk. 

 In the cow there is a large milk cistern associated with each 

 of the four teats, which in this animal, as in so many others, arise 

 from an udder or bag containing the mammary glands. The 

 walls of the ducts, as well as some at least of the alveoli, are 



