Answer
Valves are more important in veins of arms and legs (free extremities) than veins of the neck because of the action of gravity. When one is standing, gravity causes a pooling of blood in the free limbs, but aids the flow of blood from the neck veins back to the heart.
Work Step by Step
Venous valves are folded portions of the tunica interna of veins. The flap-like cusps of these valves project ot into the lumens (lumina) of the veins in the direction of the heart. Venous valves aid in venous return by closing when blood tries to flow backward. In the free limbs, the pull of gravity works against venous blood return, but in the neck the pull of gravity aids the return of venous blood to the heart.
