100 THE CHEST. 



of the subclavian and the thoracic aorta, the phrenic, 

 mediastinal, and intercostal branches of the internal 

 mammary, and the thoracic branches of the axillary. 



The nerves are the intercostals and phrenics. 



Mammary Glands. On the outside of the chest walls, 

 lodged in the fascia of the pectoral muscles, are the 

 mammary glands, accessory organs of the generative 

 system. They exist in both sexes but are only rudimen- 

 tary in the male. In the female they are small before 

 puberty but enlarge as the generative organs become 

 more completely developed, forming two hemispherical 

 eminences, one on either side, between the third and 

 seventh ribs. During pregnancy they increase once more 

 in size preparatory to the secretion of the milk, and in 

 old age they atrophy. From the middle projects a small 

 pinkish-brown conical eminence, the nipple, surrounded 

 by a paler area, the areola. After the second month of 

 pregnancy both nipple and areola become darker in color, 

 a point of great diagnostic value in early pregnancy. 



The mammary glands themselves consist of lobules of 

 gland tissue with a central lactiferous tubule, the lobules 

 being gathered into lobes with fatty tissue between. 

 From the juncture of these tubules result fifteen or 

 twenty excretory ducts, the tubuli lactiferi, which con- 

 verge toward the areola. Beneath the nipple they dilate, 

 forming the ampullce, and then contract again to pass out 

 through the nipple as straight tubes. 



Breast abscess occurs most commonly in nursing 

 mothers, as where a part is most active there is most dan- 

 ger of abscess. Many benign tumors of the breast, as the 

 fibrous tumors, occur and are especially common in 

 young women. If a fibrous tumor is allowed to develop 

 it may become cancerous. Cancer, however, generally 

 occurs after the age of forty and is usually due to some 

 irritation, as to a blow from a ball. 



The arteries of the breasts are the thoracic branches of 

 the axillary, the intercostal, and the internal mammary. 



The nerves are from the thoracic cutaneous. 



