172 BIOLOGY OF THE LABORATORY MOUSE 



and blood vessels so that the stroma and blood vessels are in intimate contact 

 with the tumor cells. The main object in this classification is to separate a 

 large group of malignant tumors from the carcinomas; however, this method 

 ignores certain embryological considerations. A carcinoma is a malignant 

 tumor originating from the epithelial cells of the skin, the mucosa or their 

 derivatives. In general, sarcomas present a smooth, rounded contour, while 

 the carcinomas appear less uniform in consistency and frequently give a 

 nodular appearance. 



Histological Classification of Mouse Tumors 



I. Connective tissue (types i through 7 are benign). 



1. Fibroma — connective tissue origin. 



2. Myxoma* — mucous connective tissue origin. 



3. Lipoma — fat tissue origin. 



4. Chordoma* — Chorda dorsalis tissue origin. 



5. Chondroma — cartilage tissue origin. 



6. Osteoma — bone tissue origin. 



7. Angioma 



a. Hemangiona — blood vessel origin. 



b. Lymphangioma — lymph vessel origin. 



8. Sarcoma — a mahgnant cellular tumor composed of anaplastic 

 tissue of any of the above types i through 7. 



a. Fibrosarcoma. 



b. Neurogenic sarcoma. 



c. Myxosarcoma. 



d. Liposarcoma. 



e. Chondrosarcoma. 



/. Osteogenic sarcoma. 



g. Angio-endothelioma. 



h. Round cell sarcoma. 



(i) Lymphocytoma. 



(2) Myelocytoma. 



(3) Monocytoma. 

 II. Muscle tissue. 



I. Myoma (benign). 



a. Leiomyoma — smooth muscle tissue origin. 



b. Rhabdomyoma — striated muscle tissue origin. 



* As yet not reported in mice. 



