Abstract: A surgical instrument for making a closed periphery incision, preferably navicular in shape, comprises a handle including an enlarged cutting head rigidly mounted at one end thereof to prevent relative rotation between the handle and the cutting head, the head being hollow and defining a pair of elongated cutting blades arranged in generally side-by-side relation and including cutting edges therealong facing in generally the same direction, corresponding pairs of ends of the blades being convergent toward and joined with each other, and the cutting edges being outwardly convex in the direction in which they face. By virtue of at least one pair of corresponding blade edges intersecting to form an acute angle included therebetween, the incision is advantageously started by applying the corner defined by the intersecting blade edges to the skin with a firm pressure and then rocking the tool along its outwardly convex edges to complete the incision.