The height, the size and the interval space of the valves of the vena saphena magna and the ductus thoracicus of adult dogs were measured. As a result it was found that except for a slight difference the height of the valves could be represented by 1/4 wave length, and the interval space between the upper margins of the valves by 1/2 wave length. Such a slight difference seems to be due to the difference in the growth of the venous and thoracic duct wall. From the vascular structure the structural mechanisms of the valves have been described hemodynamically.