The ornamental design for a medical dressing, as shown and described.
FIG. 1 is a perspective view of the new design for a medical dressing;
FIG. 2 is a front elevational view thereof, the back elevational view being a mirror image of the front elevational view;
FIG. 3 is a right side elevational view thereof, the left side elevational view being a mirror image of the right side elevational view;
FIG. 4 is a top plan view thereof; and,
FIG. 5 is a bottom plan view thereof.
The broken lines shown in FIGS. 1-5 illustrate portions of the medical dressing that form no part of the claimed design. In addition, the surface shading illustrated in the drawings is provided merely to highlight the contour of design; it is not intended to be illustrative of texture or gloss.