THE MAMM.E ItDTl 



and is capable of a kind of erection undtr the influence of cold, mechanical 

 stimulus, or mental emotion. In some jjcrsons it is normally retracted into a 

 dei»ression of the integument, and only projects in response to stimulation. 



The areola is ahout an inch in diameter, and is characterised l»y its pifrmentation, 

 the delicacy of its texture, the absence of subcutaneous fat, the large development 

 of its sebaceous and accessory milk glands, and its contractility under the inllu- 

 enees wliich produce erection of the nipple. It is pink in the virgin, l)ut during 

 ]»r<'gnancy and lactation assumes a brownish shade. The accessory glands, slightly 

 marked in the virgin, form distinct prominences after impregnation (tubercles of 

 Montgomery). 



The contractility of tlie nii)i)le and areola is due t(^ the presence of circular 

 and radiating fibres of unstriped muscle in the subcutaneous tissue, the former 

 passing into the substance of the nipple, and forming a network around the lactif- 

 erous ducts. The circular tibres by their contraction cause the nipple to project; 

 the radiating filjres retract it. 



Variations according to age and functional activity. — At birth the gland is 

 only about onivfifth to onc-tliinl of an inch in diameter. The nipple with its 

 dartos is well formed, and the secreting structure is represented by slightly ramified 

 ducts which contain a milky fluid. Growth is slow up to the time of jaibcrty; 

 after tliis. development progresses rapidly, l)ut no distinct indication of subdivision 

 into lobes is present until impregnation takes place. Some sliglit engorgement of 



Fig. 658.— Develop.mext of the Mamma of the Female Embryo. 

 (7 inches in length X 70.) (After Langer.) 





j^m 



the breast may, however, occur at the menstrual i)eriod, when a yellowish glutinous 

 secretion may sometimes be expelled from the ducts. In pregnancy and during 

 lactation the evolution of the gland-structure is remarkably active. The whole 

 breast enlarges, the superficial fat undergoes alisorption, the vessels become dilated 

 and their walls thickened; the areola and nipple increase in size, and the former 

 becomes more or less deeply pigmented. After the end of lactation the lireast 

 l)ecomes smaller, but seldom resumes its original condition of smoothness, firmness, 

 and elasticity, and some traces of the pigmentation of the areola remain permanent. 

 In old age the glandular structures atn>phy. 



The male breast diflfers fn.m that of the female in the early arrest of its ev(tlu- 

 tion. It ranges in diameter from a third of an inch to an inch, and posses.ses an 

 areola and a nipple, the former often beset with hairs. It is usually jilaced over the 

 fourtli intercostal sjjace, a little internal to tiie l»order of the pecttjrahs major, but 

 its petition is very variable, and the two glands are often unsynnnetrical. A tem- 

 ])orary engorgement occasionally appears in early adult life, and may lead to 

 inHammatory complications. 



Vessels and nerves. — The arteries are derived from the internal mammary 

 through the si'cond. tliinl. and fourth intercostal spaces, and from the thoracic 

 In-anches of the axillary. The chief supi)ly is given to the perforating branclu-s of 

 the internal mannnary, but the external mannnary l)ranch of the axillary artery may 

 be of large size in the female. 



