324 



TUMORS. 



vessels or spaces. In this case its genetic relationship may throw light 

 on the nature of the tumor, however similar it may be in morphology to 

 carcinoma. 



Sometimes the cells of the endotheliomata are packed together in 

 dense concentric masses (Fig. 167), which may have a glistening appear- 

 ance, and such tumors are sometimes called cholesteatotiiata. Although, 

 for the most part, the peculiar glistening appearance of these tumors is 

 due to the closely packed thin cells which compose them, they not infre- 

 quently contain crystals of cholesterin, which may share in producing 



FIG. 169. ENDOTHELIOMA OF UPPER JAW. 



Showing formation of mucus in the gland-like endothelial cell masses. This form of tumor is often called 



" cylindroma." 



this characteristic appearance. But the cholesterin may be absent, or 

 present in small amount. 



The stroma of the endotheliomata may undergo various forms of 

 alteration, developing hyaliu, myxomatous, or cartilaginous or very 

 dense fibrous characters (Fig. 164) ; or it may atrophy, leaving the pro- 

 liferated endothelium and the blood-vessels as the chief structural ele- 

 ments. On the other hand, hyalin and mucous degeneration of the endo- 

 thelial cells may occur (Fig. 168), and considerable collections of these 

 materials, free from the cells but surrounded by the cell masses, may 

 give a cyStic character or lend a glandular appearance to the growth. 



Such tumors in which homogeneous or striated cylinders of hyalin 

 or mucoid material (Fig. 169), often closely surrounded by layers of 

 cuboidal or flattened cells (Fig. 165), form a striking feature have 

 sometimes been called cylindromata. The stroma of the eudothelionia 



