THE SKIN AND TTS APPEXDAGES 4().S 



(lobular ducts), one of which runs to each lobule. Within the latter 

 the lobular duct breaks up into a number of terminal ducts, which in 

 turn open into groups of alveoli. The lifteen to twenty main excre- 

 tory ducts pass through the nipple and open on its surface. At the 

 base of the nipple each main duct presents a sac-like dilatation, the 

 ampulla, which appears to act as a reservoir for the storage of the 

 milk. 



m 



'&■■ 







_^i 



Fig. 284. — From Section of Human Inactive Mammary Gland. X25. (Technic 

 I, p. 407.) Gland composed almost wholly of connective tissue; few scattered groups 

 of tubules. 



Until puberty the gland continues to develop alike in both sexes, 

 but after about the twelfth year the male gland undergoes retrogres- 

 sive changes, while the female gland continues its development. 



The inactive mammary gland, by which is meant the female 

 gland up to the advent of the first pregnancy and between periods of 

 lactation, consists mainly of connective tissue and a few scattered 

 groups of excretory ducts (Fig. 284). Around the ends of some of 

 the ducts are small groups of collapsed alveoli. Both ducts and alve- 

 oli are lined with a low columnar, often rather flat epithelium. In 

 some cases the flat cells are two or three layers thick, forming a thin 

 stratified squamous epithelium. The relative amount of fat and 



