FIG. 1 is a front perspective view of a surgical knife showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a top plan view thereof;

FIG. 5 is a bottom plan view thereof;

FIG. 6 is a right side elevational view thereof; and,

FIG. 7 is a left side elevational view thereof.

The broken lines in the drawings are shown for illustrated purposes only and form no part of the claimed design. The dot-dashed lines denote the boundary of the claim, and form no part of the claimed design.