438 THE FEMALE EEPKODUCTIVE ORGANS 



ker*) lobes, each of which is of itself a tubulo-acinar gland whose 

 lactiferous duct opens on the surface of the nipple near its apex. 

 The mouths of these ducts are narrow : their terminal portions in 

 the deeper part of the mammilla are much broader, thus forming 

 in each lobar duct a sort of terminal saccule or lactiferous sinus. 

 The main lactiferous ducts subdivide in an 'arborescent manner 

 into many interlobular ducts, about which are clustered the groups 

 of secreting alveoli, each group forming one of the many lobules 

 included in a lobe of the gland. The structure of the lobule, 

 as well as the general appearance of microscopical sections of the 

 gland, varies much according to the stage of development and the 

 condition of activity of the organ. 



THE ACTIVE GLAND. During lactation the glandular alve- 

 oli are so numerous as to form by far the most prominent portion 

 of the gland. Each lobule consists of a cluster of saccular alveoli 

 which open by short alveolar ducts into the interlobular ducts of 

 the connective tissue which invests the lobules of the gland. The 

 alveoli are closely packed within the lobule. In form, except for 

 the regularity of their epithelium and the distinctness of their cell 

 outlines, they might well be compared with the intralobular alveoli 

 of the salivary glands. They possess, however, a broader lumen. 



The actively secreting alveoli are lined by cuboidal or low col- 

 umnar cells which vary much in height even within the same 

 alveolus, and are often considerably flattened. Their secretory 

 activity is indicated by the appearance of fat droplets, which ac- 

 cumulate within the distal portion of their cytoplasm. These 

 droplets apparently push toward the free surface of 'the cell, gain- 

 ing somewhat in size as well as in number, until they finally occupy 

 the greater part of the distal end of the cell and are separated 

 from each other by only a narrow interval of albuminous cyto- 

 plasm. At last they are discharged into the broad lumen of the 

 alveolus, where they apparently still retain a thin albuminous 

 envelope which prevents their cohesion and consequent fusion, and 

 thus permits their suspension in the albuminous, fluid portion of 

 the milk. 



The spheroidal nuclei of the secreting cells during this process 

 are crowded to the base of the cell, and after the discharge of the 

 secretion the shrunken but nucleated cell remnants remain in 

 situ ; after a period of rest, the cells apparently resume their 

 secretory function. It appears probable that each cell in its life 



* Handbuch, iii, 590. 



