A malignant tumor of the bone which always arises in the medullary tissue, occurring more often in cylindrical bones. There are conspicuous foci of necrosis in association with irregular masses of small, regular, rounded or ovoid cells with very scanty cytoplasm. The tumor occurs usually before the age of 20, about twice as frequently in males as in females. (From Dorland, 27th ed; Stedman, 25th ed).