GENERATIVE ORGANS OF THE FEMALE. 



215 



At each menstrual period the greater part of the mucous membrane 

 of the body undergoes a process of disintegration accompanied by an 

 escape of blood from the capillaries of the membrane. This is suc- 

 ceeded by a rapid renewal of the membrane. Should gestation super- 

 vene, the process of renewal results in the formation of a greatly 

 thickened mucous membrane, with long convoluted glands, which is 

 then known as the decidua. 



The mammary glands are compound racemose glands which open 

 by numerous ducts upon the apex of the nipple. The ducts are dilated 

 into small reservoirs just before reaching the nipple. If traced back- 

 wards, they are found as in other compound racemose glands to com- 

 mence in groups of saccular alveoli. The walls of the ducts and alveoli 

 are formed of a basement-membrane lined by a simple layer of flattened 

 epithelium (fig. 249, A). But during lactation, when the gland is in 

 activity, the cells of the alveoli become much enlarged and of a 

 columnar shape, and fatty globules become formed within them (B). 

 These fatty globules appear to become set free by the breaking down 

 of the inner part of the cell, the protoplasm of the cells becoming 



FIG. 249. ALVEOLI OF THE MAMMARY GLAND OF THE BITCH UNDER DIFFERENT 

 CONDITIONS OF ACTIVITY. (Heideiihain. ) 



A, section through the middle of two alveoli at the commencement of lactation, the epithelium- 

 cells being seen in profile ; B, an alveolus in full secretory activity. 



partially dissolved and forming the proteid substances of the milk. 

 According to Rauber, lymph-corpuscles may also carry fat into the 

 alveoli and there 1 become disintegrated. At the commencement 

 of lactation the disintegration of the cells is imperfect, so that 

 numerous cells containing fat-particles appear in the secretion (colostrum 

 corpuscles). 



