The ornamental design for a mountingtab for a cranial implant, as shown and described.
FIG. 1 is a top front-right isometric view of a mounting tab for a cranial implant showing our new design;
FIG. 2 is a bottom front-left isometric view thereof;
FIG. 3 is a left side view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a front view thereof;
FIG. 6 is a rear view thereof;
FIG. 7 is a top view thereof; and,
FIG. 8 is a bottom view thereof.
The broken line showing of the hole indicates unclaimed subject matter and the broken line showing of the attached member indicate environment and form no part of the claimed design.