FIG. 1 is a top front left perspective view of a spinous process reamer showing my new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a left side elevation view thereof;

FIG. 5 is a right side elevation view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view thereof.

The ornamental design for a surgical instrument for preparing the spinous process to receive a surgical implant.