We claim, the ornamental design for a catheter, as shown and described.
FIG. 1 is a front view of a catheter, showing our new design;
FIG. 2 is a rear view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a bottom plan view thereof;
FIG. 5 is a left side view thereof; and,
FIG. 6 is a right side view thereof;
FIG. 7 is a reduced-scale front view showing the catheter in a wound condition.
The broken lines shown in the drawings represent portions of the catheter that form no part of the claimed design. The parallel dash-dot lines in the drawings indicate that the appearance of any portion of the catheter between the break lines forms no part of the claimed design.