The ornamental design for a catheter, as shown and described.
FIG. 1 is a front perspective view of a catheter;
FIG. 2 is a front view of the catheter;
FIG. 3 is a rear view of the catheter;
FIG. 4 is a right side view of the catheter;
FIG. 5 is a left side view of the catheter;
FIG. 6 is a top view of the catheter;
FIG. 7 is a bottom view of the catheter; and,
FIG. 8 is an enlarged view of a tip of the catheter.
The broken lines shown throughout the views represent the portions of the catheter which form no part of the claimed design. Aspects of the catheter, including individual tubes and the multi-lumen section, are flexible. The catheter is shown with a symbolic break in its length. The appearance of any portion of the article between the break lines forms no part of the claimed design.