310 



VETERIXAR\- rATlIOLOGY. 



two portions. One portion is visually composed of spindle cells 

 which are connected into dense bands extending in various direc- 

 tit)ns and forming alveoli ; hence the name alveolar. The other 

 portion of the stroma is intercellular and corresponds to that of 

 the round-cell sarcoma. The arrangement of the cells into nests 

 is suggesti\c of a carcinoma, but the differentiation is not diffi- 

 cult and depends upon ; first, the presence of intercellular sub- 

 stance between the cells which is present in sarcomata but is 

 absent in carcinomata ; second, sarcomatous cells are embrvonic 

 connective tissue cells and hence contain nuclei relatively large 

 in proportion to the size of the cell, while carcinomatous cells are 

 embryonic epithelial cells and contain nuclei relatively small in 

 proportion to the size of the cell. 



FiLj. 105. — Section or Alveolar Sarcoma from ovmy i 

 with sai'comatous c<.'lls. 



<^ 0[ 0' 



r lleifur sliowins 



alveoli filled 



These tumors grow slowly. They are usually encapsulated 

 and have nn tendency to form metastases. They are very mildly 

 malignant. 



Enthothelioma is a tumor ciimposed nf endothelium. This is 

 a tumor that is not specifically a sarcoma, but may be so classed. 

 Endothelium has the same origin as connective tissue, i. e., the 



