SPONTANEOUS NEOPLASMS IN MICE 



177 



a connective tissue capsule which may be thick in some places and difficult to 

 follow in others. The capsule is not invaded by the tumor cells. The 

 epithelial cells are arranged as gland-Hke structures which are easily recog- 

 nized as mammary gland in origin. These structures may vary considerably 

 in size and arrangement, but they are always lined by a single layer of fairly 

 uniform, usually small, and relatively inactive epithelial cells. Under these 



Cystic space 



Epithelium 



Stroma 



Blood vessel 



Fig. 90. — Simple adenoma of the mammary gland (X200'). 



cells the basement membrane remains intact and around this there are seen 

 a few small, thread-like, wavy, spindle-shaped connective tissue cells. 



Simple adenoma of the mammary gland. — This is not commonly seen as 

 such, but it is not rare to observe the remains of this type in direct continuity 

 with carcinoma of the mammary gland. These adenomas contain gland-like 

 arrangements of the mammar\^ epithelial cells (Fig. 90). They range from 

 small abortive structures which appear to be attempts at gland formation to 

 large, round or oval, dilated cyst-like spaces containing more or less eosino- 

 philic amorphous material. The lining cells are arranged in a single, smooth, 

 orderly layer. Generally they are cuboidal and uniform in size, shape and 



