Physiologists who followed the time of Harvey realized that the ventricular force exerted in systole is good enough to take blood to the terminal arterioles into the capillaries and then vanish. If ventricular force was the sole force of circulation, the weight of the venous column of blood would neutralize and stagnation of blood in the venous system would occur. A large volume of venous plexus is embedded in these muscles. Bollinger et al. in 1970 observed another important force aiding in the venous return of blood to the right atrium. During expiration the diaphragm moves up, decreasing intra-abdominal pressure, and the blood from the femoral veins of the lower extremities moves into the inferior vena cava. Since the work of Sir William Harvey over the last 400 years, there have been only two adjunctive forces identified and added to the explanation of the motion of blood in the venous tree.