194 BIOLOGY OF THE LABORATORY MOUSE 



region. At least this is true for our mice and according to the pubHshed 

 literature from other sources. 



Angiomas. — These tumors are found especially in the C57 black stock 

 mice. This is true for both hemangiomas and lymphangiomas. The former 

 has been mistaken for primary carcinoma of the mammary gland on super- 

 ficial inspection of the living mouse. Even on gross section it may resemble 

 somewhat the mammary gland tumors with dilated, blood-filled cysts. 



Hemangiomas may be formed anywhere in the mammary gland region. 

 They are composed of the elements of blood vessel walls and develop as a 

 benign tumor with a poorly formed capsule. Lymphangiomas, on the other 

 hand, are found in the axillarv^ or the inguinal regions. They are benign 

 tumors formed from the elements of the lymph vascular system. 



Lipomas. — These are tumors of adipose tissue. They are benign tumors 

 with cells larger than normal and without the vascular arrangement of 

 normal fat tissue. 



Fibrosarcoma. — This growth may occur near the mammar\' glands and 

 may invade and destroy them. Here the epithelium is not a part of the 

 tumor. The tumor has spread around the normal tissue as is the case in the 

 infiltration of other normal tissues. Fibrosarcoma here is the same as that 

 which will be described later under subcutaneous fibrosarcoma (Fig. 112). 



Melanoma. — This is a pigmented tumor sometimes seen at the base of 

 the tail in the dba females which are of a high mammary tumor stock. How- 

 ever, the tumor is usually black and not confused grossly with a mammary- 

 carcinoma, even when the latter has blood filled cysts. 



Rhabdomyosarcoma. — This is a sarcoma of the striated muscles and has 

 been found in the mammary gland region of dba stock female mice. The 

 same is true of hybrids between the dba and C57 black stocks. 



Osteogenic sarcomas and chondrosarcomas. — Sarcomas of bone origin in 

 the mammary region are uncommon in our stocks. One chondrosarcoma 

 originating from rib cartilage has been noted. As stated under the sub- 

 cutaneous tumors, osteogenic sarcoma has occurred several times. J. A. 

 Murray (43) reported on a chondro-osteosarcoma in the left groin of a female 

 mouse. Pybus and Miller (45) developed a branch of the Simpson strain 

 with a fairly high incidence of bone sarcomas, several of which were in the 

 mammary region. 



Carcinoma of skin appendage. — These arise from specialized sebaceous 

 glands. The preputial (23) and clitoral glands also fall into this group. 

 This carcinoma can be traced to the skin appendage glands as its site of 

 origin (Fig. 109). 



