NAEVUS, a term in surgery signifying that form of tumour which is almost entirely composed of enlarged blood-vessels. There are three principal varieties: (1) the capillary naevus, consisting of enlarged capillaries, frequently of a purplish colour, hence the term “port-wine stain”; (2) the venous naevus, in which the veins are enlarged, of a bluish colour; (3) the arterial naevus, in which there is distinct pulsation, it being composed of enlarged and tortuous arteries. The naevus can be lessened in size by pressure. It generally occurs in the skin or immediately under it; sometimes it lies in the mouth in connexion with the mucous membrane. It is often congenital, hence the term “mother’s mark,” or it may appear in early childhood. It often grows rapidly, sometimes slowly, and sometimes growth is checked, and it may gradually diminish in size, losing its vascularity and becoming fibrous and non-vascular. This natural cure is followed by less deformity than a cure by artificial means. Various methods are used by surgeons when an operation is called for: (1) the tumour may be excised; (2) a ligature tightly tied may be applied to the base of the tumour; (3) inflammation may be set up in the growth by the injection of irritating agents,—in this way its vascularity may be checked and the formation of fibrous tissue encouraged; (4) the blood in the enlarged vessels may be coagulated by the injection of coagulating agents or by electrolysis.