ANATOMY OF THE MAMMARY GLANDS. 



329 



covered in front by a subcutaneous layer of fat, and posteriorly it is envel- 

 oped in a fibrous membrane loosely attached to the pectoralis major muscle. 

 A considerable quantity of adipose tissue is also found in the substance of 

 the gland between the lobes. 



Separated from the adipose and fibrous tissue, the mammary gland is 

 found divided into lobes, fifteen to twenty-four in number. These are 

 subdivided into lobules made up of a greater or less number of acini, or 

 culs-de-sac. The secreting structure is of a reddish-yellow color and is 

 distinctly granular, presenting a decided contrast to the pale and uniformly 

 fibrous appearance of the gland during the intervals of lactation. If the 

 ducts be injected from the nipple and be followed into the substance of the 

 gland, each one will be found distributing its branches to a distinct lobe; so 

 that the organ is really made up of a number of glands identical in structure. 



The canals which discharge the milk at the nipple are called lactiferous 

 or galactophorous ducts. They are ten to fourteen in number. The open- 

 ings of the ducts at the nipple are very small, measuring only -fa to ^ of an 

 inch (0-42 to 0-64 mm.). As each duct passes downward, it enlarges in the 

 nipple to -fa or ^ of an inch (1 or 2 mm.) in diameter, and beneath the are- 

 ola it presents an elon- 

 gated dilatation, $ to J 

 of an inch (4-2 to 8-5 

 mm.) in diameter, called 

 the sinus of the duct. 

 During lactation a con- 

 siderable quantity of milk 

 collects in these sinuses, 

 which serve as reservoirs. 

 Beyond the sinuses, the 

 caliber of the ducts meas- 

 ures ^ to -J- of an inch 

 (2-1 to 4-2 mm.). The 

 ducts penetrate the dif- 

 ferent lobes, branching 

 and subdividing, to ter- 

 minate finally in the col- 

 lections of culs -de- sac 

 which form the acini. 

 There is no anastomosis 

 between the different lac- 

 tiferous ducts, and each 

 one is distributed inde- 

 pendently to one or more 

 lobes. 



The lactiferous ducts have 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 lon- 



FIG. 102. Mammary gland of the human female (Ltegeois). 

 a, nipple, the central portion of which is retracted; &, areola ; c, c. 

 c, c, c, lobules of the gland: 1. sinus, or dilated portion of one of 

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



