"The posterior tibial veins, located in the lower legs, are considered among the major systemic veins of the human body.
They originate from the foot veins behind the medial malleolus, which is part of the group of nerve tissue and muscle that surround the ankle joint. They run up the medial, or inner, sides of the calves to just below 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."