356 



HISTOLOGY OF THE MORBID PROCESSES. 



Endotheliomata, on the other hand, spring from the connective tis- 

 sues, often at a point remote from any epithelial structures ; e. g. 9 

 the dura mater. 



When the endothelioma owes its origin to a proliferation of the 

 flat cells lining the lymph-spaces or vessels it has a plexiform struct- 

 ure, the young cells occupying pre-existent interstices in the tissues 

 or following the arrangement of the vessels (Figs. 318 and 319). 

 As the cells grow older they may become flattened, and are then 



-,-; " S : :<.-. ;-.--,.;; ,V 



M i W 





Endothelioma from the floor of the mouth. (Earth.) Older portion of the growth. This 

 has a general alveolar structure, the alveoli being separated by a vascularized areolar 

 tissue, n, n, necrosed groups of endothelial cells ; h, h, similar necrosed masses that have 

 undergone hyaline degeneration. 



often imbricated, forming little, pearl-like bodies. These may 

 subsequently undergo degenerative changes, such as hyaline degen- 

 eration, which convert them into homogeneous masses or bands. 

 Where this takes place the tumor has received the name, " cylin- 

 droma." Or the degenerated cells may be the seat of calcareous infil- 

 tration. This is the origin of the psammomata or " sand-tumors " of 

 the cerebral membranes (Fig. 320). In other cases the cells may 

 not acquire the membranous character of adult endotheliurn, but 

 continue to multiply without such specialization. Then the tumor 

 partakes of the sarcomatous nature of the other connective-tissue 

 tumors of highly cellular structure and devoid of any marked 



