MAMMARY GLANDS. 77 



of simple follicles, as they are described by most anatomists. 1 

 The nipple contains the lactiferous ducts, fibres of inelastic 

 and elastic tissue, with an immense number of non-striated 

 muscular fibres. The muscular fibres have no definite direc- 

 tion, but are so numerous, that when they are contracted, 

 the nipple becomes very firm and hard. The nipple, though 

 it may thus become hard upon the application of cold or 

 other stimulus, presents none of the anatomical characteris- 

 tics of the true erectile organs, as is erroneously supposed by 

 some authors ; and its hardening is simply due to contrac- 

 tion of its muscular fibres. 8 



The areola does not lie, like the general integument 

 covering the gland, upon a bed of adipose tissue, but is 

 closely adherent to the subjacent glandular structures. The ' 

 skin here is much thinner and more delicate than in other 

 parts, and the pigmentary granules are very abundant in 

 some of the lower" strata of epidermic cells, particularly dur- 

 ing pregnancy. The true skin of the areola is composed of 

 inelastic and elastic fibres, and lies upon a distinct layer of 

 non-striated muscular fibres. The arrangement of the mus- 

 cular fibres (sometimes called the sub-areolar muscle) is quite 

 regular, forming concentric rings around the nipple. These 

 fibres are supposed to be useful in compressing the ducts 

 during the discharge of milk. The areolar presents nu- 

 merous papillae, considerably smaller than those upon the 

 nipple ; hair-follicles, containing small, rudimentary hairs ; 

 sudoriparous glands ; and sebaceous glands connected with 

 the hair-follicles. The sebaceous glands in this situation 

 are very large, and their situation is indicated by little 

 prominences at the surface of the areola, which are especi- 

 ally marked during pregnancy. 



The gland itself is of the compound racemose variety. 

 It is covered in front by a subcutaneous layer of fat, and 

 posteriorly is enveloped in a fibrous membrane loosely at- 



1 SAPPEY, Traite cT anatomic descriptive, Paris, 1857, tome iii., p. 594. 



2 For the anatomy of the erectile tissues, see vol. i., Circulation, p. 336. 



