358 HISTOLOGY OF THE MORBID PROCESSES. 



designated as an angiosarcoma or alveolar sarcoma, according as the 

 cells show a grouping around the vessels or form collections occu- 

 pying the meshes between them (Figs. 321, 322, and 323). 



This brief outline of a complicated group of tumors will serve 

 to show that some members of that group closely simulate epi- 

 theliomata in their structure, though they are quite different in their 



FIG. 321. 



Endothelioma of the ulna. (Driessen.) a, a, alveoli lined with endothelial cells and occupied 

 by blood; 6, areolar tissue between the alveoli, containing capillary vessels, c; d, large 

 vessel closely surrounded by proliferated endothelium. The structure of this tumor is 

 difficult of interpretation. It appears most probable that its origin lay in the prolifera- 

 tion of the endothelium of lymphatics, and that the blood in a, a is due to commumca- 

 .tions established between the bloodvessels and elongated and anastomosing alveoli of 

 the tumor. The cells of this growth contained glycogen (see Fig. 249). 



origin ; while other members of the group are essentially sarcomata, 

 owing their origin to a particular variety of connective-tissue cells 

 and having peculiarities of structure due to the situations in which 

 those cells normally occur. The significance of the tumor will 

 depend in each case upon its tendency to grow rapidly and to infil- 

 trate the surrounding tissues, and its liability to metastasis. These 

 qualities must be estimated by a consideration of the history of 



