PHYSIOLOGICAL ANATOMY OF THE MAMMARY GLANDS. 367 



other. It will be most convenient, in studying the intimate structure of the gland, to 

 begin at the nipple and follow out one of the ducts to the termination of its branches in 

 the secreting culs-de-sac. 



The canals which discharge the milk at the nipple are called lactiferous or galac- 

 tophorous ducts. They vary in number from ten to fourteen. The openings of the ducts 

 at the nipple are very small, measuring only from --$ to ^ of an inch. As each duct 

 passes downward, it enlarges in the nipple to ^ or T * of an inch in diameter, and beneath 

 the areola it presents an elongated dilatation, from $ to |-of an inch in diameter, called the 

 sinus of the duct. During lactation, a considerable quantity of milk collects in these sinuses, 

 which serve as reservoirs. Beyond the sinuses, the caliber of the ducts measures from 

 yV to of an inch. They penetrate the different lobes, branching and subdividing, to 

 terminate finally in the collections of culs-de-sac which form the acini. Most modern 

 observers are agreed that there is no anastomosis between the different lactiferous ducts, 

 and that each one is distributed independently to one or more lobes. 



r 



FIG. 102. Mammary gland of the human female, (Liepeois.) 



a, nipple, the central portion of which is retracted ; 6, areola; c, c, c. c, c, lobules of the pland : 1, sinus, or dilated 

 portion of one of the lactiferous ducts; 2, extremities of the lactiferous ducts. 



The intimate structure of the lactiferous ducts is interesting and important. They 

 are possessed of three distinct coats. The external coat is composed of anastomosing 

 fibres of elastic tissue, with some inelastic fibres. The middle coat is composed of non 

 striated muscular fibres, arranged longitudinally and existing throughout the duct, froip 

 its opening at the nipple to the secreting culs-de-sac. The internal coat is an amor 

 phous membrane, lined with roundish or elongated cells during the intervals of lactation 

 and even during pregnancy, but deprived of epithelium during the period when the lac- 

 teal secretion is most active. 



The acini of the gland, which are very numerous, are visible to the naked eye, in the 

 form of small, rounded granules, of a reddish-yellow color. Between these acini, there 

 exist a certain quantity of the ordinary white fibrous tissue and quite a number of adi- 



