tumor. A swelling or tumefaction.

Tumors of Bone. All the primary tumors of bone are of the connective tissue group, but various secondary tumors of epithelial origin may occur.

Osseous tumors may arise from the periosteum or from the marrow. If they arise from the periosteum they may extend early to the adjacent soft tissues and involve and destroy them. If the tumor arises in the marrow, it is for a long while cut off from the adjacent soft tissues by the thick cortex, and about the extending medullary tumor may also come a reactive proliferation by the periosteum, so that as the tumor extends it still may, for a long time, be surrounded by a shell of bone which prevents infection of the soft parts. After a time, however, the reactive periosteum shell usually becomes perforated at one or more points, and then the medullary tumor extends to the adjacent tissues. The cause of these tumors is absolutely unknown.