valve of lymphatics, any one of the tiny semilunar structures in the vessels and trunks of the lymphatic system that helps regulate the flow of lymph and prevents venous blood from entering the system. There are no valves in the capillaries of the system, but there are many in the collecting vessels. The valves are attached by their convex edges to the walls of the vessels, leaving their concave edges free and directed along the course of the current of lymph. Usually two valves of equal size are found opposite each other. They are more numerous near the lymph nodes and more prevalent in the lymphatic vessels of the neck and the arms than in the vessels of the legs. The wall of the vessel just above the attachment of each valve bulges with a small sinus that gives the vessel its beaded appearance. See also lymphatic system.
