The peripheral venous system is subdivided into a superficial (epifascial) and a deep (subfascial) system by the superficial fascia. The two systems are interconnected by the transfascial system, called perforanting veins. The blood from the superficial system (great saphenous vein and small saphenous vein) is drained to the deep system. The deep veins accompany the arteries. The direction of venous blood flow is controlled by valves. The number of valves is variable. The veins are surrounded by a venous sheath in which they are movable. The deep veins of the lower leg are arranged in three groups consisting of paired veins. The peroneal vein and the posterior tibial vein unite to form the tibioperoneal trunk. The tibioperoneal trunk is joined by the anterior tibial vein to form the popliteal vein. The superficial femoral vein which arises from the popliteal vein is joined by the deep femoral vein to form the common femoral vein. The latter vessel becomes the external iliac vein above the inguinal ligament. It unites with the internal iliac vein to form the common iliac vein. Both common iliac veins unite to form the inferior vena cava. The veins of the systemic circulation perform two basic tasks, returning venous blood to the heart and storing the blood volume that is not immediately needed. Several factors like venous valves, thoracoabdominal venous pump and peripheral venous pump are necessary to maintain venous return. The second task results from the elastic compliance of the venous system, especially the mesenteric channels.