422 PHYSIOLOGY. 



which in turn are subdivided into lobules. The lobules and lobes are 

 held together by means of fibrous tissue, while between the lobes are 

 septa. 



The mammary gland-tissue, in general, when free from fibrous 

 tissue and fat, is of a pale-reddish color, firm in texture, and circular 

 in form. The smallest lobules consist of a cluster of rounded vesicles., 

 which open into the smallest branches of the lactiferous ducts. 

 These small ducts unite to form larger ducts, which later terminate 

 in a single canal. This latter corresponds with one of the chief sub- 

 divisions of the gland. 



These main excretory ducts, about fifteen or twenty in number^ 

 are termed tubuli lactiferi. These present in their course a general 

 convergence toward the areola, beneath which they form dilata- 

 tions: ampulla?. These dilatations serve as small reservoirs for the 

 milk. During active secretion by the gland the milk collecting in 

 them distends them. Each lactiferous duct is of an average diameter 

 of one seventy-fifth of an inch, expanding into the ampullae, whose 

 average caliber is one-fourth of an inch. At the base of the nipple 

 the ampullae become contracted again to pursue a straight course to 

 its summit. Each duct pierces the nipple by a separate orifice, whose 

 opening is about one-fiftieth of an inch. The ducts are composed of 

 areolar tissue with elastic fibers and longitudinal muscular fibers. 

 T*heir mucous lining is continuous at the point of the nipple with the 

 integument. They are lined internally by short columnar, and, near 

 the nipple, by flattened epithelium. 



With the exception of the nipple, the general surface of the 

 mamma is covered with fat. The latter is lobulated by sheaths and 

 processes of connective tissue, which bind the skin and the gland 

 together loosely. It is by this same manner that the gland is fast- 

 ened to the great pectoral muscle beneath it. 



Blood-vessels, nerves, and lymphatics are plentifully supplied to 

 the mammary glands. 



The arteries are derived from the thoracic branches of the axil- 

 lary, the intercostals, and internal mammary. The veins describe,, 

 by their frequent anastomoses, a circle around the base of the nipple. 

 This has been called by Haller the circulus venosus. From this 

 branches run to the circumference of the gland. The caliber of the 

 contained vessels, as well as the size of the glands, may be increased 

 during pregnancy and lactation. The lymphatics principally run 

 along the lower border of the pectoralis major muscle to the axillary 



