Abstract: The invention relates to a retractor (10) with a carrier ring (20) and L-shaped valves (30), which can be attached with an arm (32) which runs parallel to the carrier ring plane to the carrier ring (20), whereby its free end points outward, and whose other arm (34) is oriented perpendicularly with a respect to the carrier ring plane and presents, in cross section, a convex curvature toward the external margin of the carrier ring (20), where the arm of (32) [sic; arm (32)] of the valves (30), which is attached to the carrier ring (20), is guided in radically oriented guides (22) on the carrier ring (20).