The posterior tibial veins, located in the lower legs, are considered among the principal systemic veins of the human body. They originate from the foot veins behind the medial malleolus, which is the group of nerve tissue and muscle that surrounds the ankle joint. They run up the medial, or inner, sides of the calves almost to the knees. The posterior and anterior tibial veins are classified as deep calf veins that accompany the corresponding tibial arteries of the lower legs. They are bifid veins, meaning that there are two veins for each artery. Near the knee, these veins join the peroneal trunk and become the popliteal veins. The posterior tibial veins carry blood from the fibular veins, up the legs, and to the popliteal veins. Whereas the tibial arteries supply oxygenated blood to the muscles, skin, and other tissues of the lower leg, the tibial veins carry oxygen-depleted blood away from the foot and lower leg, back toward the heart.