176 BIOLOGY OF THE LABORATORY MOUSE 



II. Tumors originating in or near the mammary line and its branches but not 

 arising from mammary glands or their stroma. 



A. Benign tumors. 



1. Fibroma. 



2. Chondroma. 



3. Osteoma. 



4. Lipoma. 



5. Angioma. 



a. Lymphangioma. 

 h. Hemangioma. 



B. Malignant tumors. 



1. Fibrosarcoma. 



2. Melanoma. 



3. Osteogenic sarcoma. 



4. Rhabdomyosarcoma. 



5. Carcinomas of skin appendage. 



6. Round cell sarcoma — axillary and inguinal lymph nodes. 



7. Endothelioma. 



a. Hemangio-endothelioma. 



b. Lymphangio-endothelioma. 



There are also non-neoplastic masses that grossly resemble true neoplasms 

 and these will be merely listed. 



1. Cysts. 



a. Mammary duct cysts. 



b. Skin cysts. 



c. Hygromas — thin-walled, endothelial-lined, cysts filled with 

 lymph. Seen in C57 black stock. 



2. Chronic inflammation. 



a. Subcutaneous in general. 



b. Chronic mastitis — fibrosis and lymphoid infiltration of the 

 mammary gland, usually not accompanied by cyst formation in 

 the mice. 



3. Lymphoid hyperplasia. 



Adenomas or the Mammary Glands 



The tumors within this benign group have certain characteristics in 

 common. Grossly they are comparatively small, frequently indistinguish- 

 able from soft non-hemorrhagic carcinomas, and sometimes they appear to 

 be soft, cystic, translucent masses. As seen under the microscope they have 



