The ornamental design for a medicalinstrument, as shown and described.
FIG. 1 is a left side perspective view of a medical instrument in accordance with the new design;
FIG. 2 is a left side elevation view thereof;
FIG. 3 is a right side elevation view thereof;
FIG. 4 is a top plan view thereof;
FIG. 5 is a bottom plan view thereof;
FIG. 6 is a front elevation view thereof; and,
FIG. 7 is a rear elevation view thereof.
The broken lines shown in FIGS. 1 and 6 are for illustration purposes only, with the lines themselves and the areas within them forming no part of the claimed design.