TUMORS. 289 



lymphangeioma of lymphatics. Corresponding to the two 

 types of muscle-tissue the tinstriped and the striped we have 

 the leiorayoma and the rhabdomyoma. 



The neuromata find their physiological prototype in the 

 nerve-fibres and ganglion-cells of the central nervous system. 



Whereas connective-tissue tumors contain DO epithelial 



tissue, in another the epithelial group, the neoplasm is 



formed almost entirely of epithelial elements, only supported 



by & framework of connective tissue. This group includes the 



apilloma, the microscopical structure of which closely resem- 



es the papillae of the skin or the villi of the intestines ; and 

 the adenoma, in which the epithelial cells are arranged in such 

 a manner as to imitate normal glandular structures with a 

 certain degree of exactitude. 



On the other hand the microscopical structure of the malig- 

 nant tumors the sarcomata and carcinomata does not 

 correspond with any normal type of tissue, but is entirely 

 atypical. 



The sarcoma is a very cellular and highly vascular connec- 

 tive-tissue tumor which histologically resembles one or another 

 stage of granulation-tissue, several varieties being described 

 according to the character of the cells of which it is formed ; 

 the small round-celled sarcoma having the microscopical ap- 

 pearances of the earliest stage of granulation-tissue ; and the 

 spindle-celled sarcoma, that of a later stage of granulation- 

 tissue as its development approaches fully formed fibrous- 

 tissue. 



The carcinoma, which is composed of epithelial cells atypi- 

 cal ly arranged in a more or less dense connective-tissue 

 stroma, is likewise described according to the character of the 

 epithelial cells of which it is composed, viz., the squamous- 

 celled carcinoma, or epithelioma ; the columnar-celled, or 

 adeno-carcinoma, and the sphei^oidal-celled, or carcinoma 

 simplex. 



AVhen a benign tumor becomes malignant it still conforms 

 to its own type of tissue ; that is to say, one of the connective- 

 tissue group becomes sarcomatous and not carcinomatous, and 

 one of the epithelial group becomes carcinomatous and not 

 sarcomatous. 



19 Hist. 



