SECRETION. 



399 



MAMMARY GLANDS. 



The mammary glands, which secrete the milk, are two more or 

 less hemispheric organs situated in the human female on the anterior 

 surface of the thorax. Though rudimentary in childhood, they 

 gradually increase in size as puberty approaches. The gland pre- 

 sents at its convexity a small conical eminence termed the mammilla 

 or nipple, surrounded by a circular area of pigmented skin, the 

 areola. The gland proper is covered by a layer of adipose tissue 

 anteriorly and is attached posteriorly to the pectoral muscles by a 

 network of fibrous tissue. 



During utero-gestation the mammary glands become larger, 



firmer, and more lobulated; the 

 areola darkens and the blood- 

 vessels, especially the veins, be- 

 come more prominent. At the 

 period of lactation the gland is 

 the seat of active histologic and 

 physiologic changes correlated 

 with the production of milk. 

 At the close of lactation these 



FIG. 1 8 1. MAMMARY GLAND, i. 

 Lactiferous ducts. 2. Lobuli of 

 the mammary gland. 



FIG. 182. ACINI or THE MAMMARY 

 GLAND or A SHEEP DURING LACTA- 

 TION, a. Membrana propria. b. 

 Secretory epithelium. 



activities cease, the glands diminish in size, undergo involution, and 

 gradually return to their former non-secreting condition. 



Structure of the Mammary Gland. Each mammary gland 

 consists of an aggregation of some 15 or 20 irregular pyramidal lobes, 

 each of which is surrounded by a framework of fibrous tissue. This 

 tissue affords support for blood-vessels, lymphatics, and nerves. 

 Each lobe is provided with a single excretory duct, the lactiferous 

 duct, which as it approaches the areola expands into a fusiform 

 ampulla or reservoir. At the base of the nipple the ampullae contract 

 to form some 16 or 18 narrow ducts, which, ascending the nipple, 

 open by constricted orifices 0.5 mm. in diameter on its apex (Fig. 181). 



