SPONTANEOUS NEOPLASMS IN MICE 173 



2. Myosarcoma (niali^naiil). 



a. Leiomyosarcoma. 



b. Rhabdomyosarcoma. 



III, Elements of the nervous system. 



1. Neuroma — nerve tiber origin. 



2. Neuroganglioma — nerve fiber and ganglion cell origin. 



3. Glioma and medulloblastoma — neuroglia tissue origin. 



4. Neuro-epithelioma -from neuro-epithelium. 



IV. Tumors of pigment cells. 



1. Melanoma. 



2. Malignant melanoma. 

 V. Endothelium. 



I. Endothelioma — blood and lymph vessel endothelium origin. 

 VI. Epithelial tissue (pavement and glandular). 



1. Papilloma — a benign tumor of pavement epithelium with support- 

 ing tissue in a normal arrangement. 



2. Adenoma — a benign tumor of glandular epithelium with supporting 

 tissue in normal arrangement. 



3. Epithelioma (epidermoid carcinoma, squamous cell carcinoma, 

 acanthoma) — a malignant tumor of pavement epithelium in atypi- 

 cal arrangement. 



4. Carcinoma — a malignant tumor of glandular epithelium in atypical 

 arrangement. 



VII. Complex tissue tumors. 



1 . Simple mixed tumor — composed of more than one type of neoplas- 

 tic tissue and named according to composition — carcinosarcoma, 

 adenofibroma, fibro-adenoma, etc. The predominating type is 

 named last. 



2. Teratoma — composed of tissues and organs of one, two or three 

 germinal layers, such as monodermal, bidermal or tridermal types. 



3. Embryoma — composed of tissues from three germinal layers in a 

 more or less orderly imitation of the fetus. 



VIII. Cysts, not neoplasms, but related to them and in mice often mistaken 

 for them by gross observation. 

 Some types of tumors have been reported in the literature as rare. How- 

 ever, our experience has been that the frequency of spontaneous tumors of 

 any particular type is dependent, to a certain extent, upon the lines of inbred 

 mice under observation. Had our observations been limited to the C57 

 black stock and other lines low in epithelial tumors of the mammary glands 



