New growths composed of endothelial cells, and arising from the intima of the blood vessels and lymphatics, are well recognized pathologic entities. They are not infrequent in the internal organs, especially in the parotid and salivary glands, and in connection with the serous membranes. It is only of recent years, however, that they have been differentiated from other and commoner neoplasms; for in appearance the endothelial cells that make up their mass vary from a large nucleated somewhat rectangular cell very like the epithelial elements of carcinoma, to a smaller, rounded cell resembling those characteristic of sarcoma. Borst1 voices the opinion, now general with pathologists, that to the class of endotheliomata undoubtedly belong many of the cases of atypical or mixed new growths which have been recorded under such names as endothelial carcinoma, endothelial sarcoma, angiosarcoma, cylindroma, fibroplastic tumor, lymphangioma, lymphatic cancroid, etc. Their differentiation from carcinomatous and sarcomatous new