?86 THE MAMMARY GLANDS. 



twenty in number, called the lactiferous or galactophorous 

 ducts, are formed by the union of the smaller ducts, and 

 open by small separate orifices through the nipple. Just 

 before they enter the base of the nipple, these ducts are 

 dilated (6, fig. 240) ; and, during lactation, the period of 

 active secretion by the gland, they form reservoirs for the 

 milk, which collects in them and distends them. The walls 

 of the gland-ducts are formed of areolar and elastic tissue, 

 and are lined internally by a fine mucous membrane, the 

 surface of which is covered by squamous or spheroidal 

 epithelium. 



Fig. 241.* 



The nipple, which contains the terminations of the 

 lactiferous ducts, is composed also of areolar tissue, and 

 contains unstriped muscular fibres. Blood-vessels are also 

 freely supplied to it, so as to give it a species of erectile 

 structure. On its surface are very sensitive papillae ; and 

 around it is a small area or areola of pink or dark-tinted 

 skin, on which are to be seen small projections formed by 

 minute secreting glands. 



Blood-vessels, nerves, and lymphatics are plentifully 

 supplied to the mammary glands ; the calibre of the blood- 

 vessels, as well as the size of the glands, varying very 



* Fig. 241. Globules and molecules of cow's milk ^. 



