I claim the ornamental design for a medical device, substantially as shown and described.
FIG. 1 is a bottom perspective view of a medical device in accordance with the present design;
FIG. 2 is top perspective view thereof;
FIG. 3 is a right side elevation view thereof;
FIG. 4 is a left side elevation view thereof;
FIG. 5 is a bottom plan view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a front elevation view thereof; and,
FIG. 8 is a rear elevation view thereof.
The features shown in broken lines in the various Figures form no part of the claimed design. The shading show contours, surfaces, or recesses of the present invention.