I claim the ornamental design for a connector for medical lines, as shown and described.
FIG. 1 shows a perspective view of a connector for medical lines showing the new design;
FIG. 2 shows a right side view thereof;
FIG. 3 shows a left side view thereof;
FIG. 4 shows a front view thereof;
FIG. 5 shows a rear view thereof;
FIG. 6 shows a top plan view thereof; and,
FIG. 7 shows a bottom plan view thereof.
The broken line showing of parts of the drawings is included for the purpose of illustrating use and environment and forms no part of the claimed design.