200 



BIOLOGY OF THE LABORATORY MOUSE 



Osteoma. — This growth originates from bone and is a benign encapsu- 

 lated tumor. It is composed mostly of dense compact bone, usually with 

 little marrow (Fig. no). This is another uncommon form of tumor and is 

 probably overlooked when small and inconspicuous. 



Lipoma. — This is a benign tumor of fat or adipose tissue and is usually 

 composed of large fat cells. The tissue looks nearly normal but lacks 



Fig. io8. — Epidermoid carcinoma of the skin. A, inguinal lymph node metastasis 

 of the carcinoma shown in Fig. io6 (X200); B. cellular detail of the tumor in Fig. 107 

 (X400). 



trabeculae, normal vascularity, and the fat cells are larger than ordinary. 

 Due to the lack of normal vascularity retrograde changes may occur, such as 

 necrosis followed by calcification. This tumor has been seen in the yellow 

 stock, in which there is a tendency for the mice to become obese. 



Angiomas. — These are benign and are composed of the elements of either 

 the blood vascular or the lymph circulatory systems. When they are 

 formed from blood vessels they are called hemangiomas, and lymphangiomas 

 when formed from lymph vessels. 



Hemangiomas grow either as a diffuse mass or as closely clustered groups 

 of endothelial lined spaces supported by a dense stroma. The endothelial 



