The ulnar veins are located in the forearm, next to the ulna bone. They are part of the venous circulatory system. The ulnar veins drain oxygen-depleted blood from the forearm. Near the elbow, these vessels join with the radial veins, forming the larger brachial veins. Eventually, all oxygen-depleted blood must move back to the heart and the pulmonary artery, where blood transits back to the lungs so that it can be replenished with fresh oxygen. Venous vessels should not be confused with arteries that have similar names. The arterial circulatory system moves oxygenated blood away from the heart. The ulnar artery takes blood from the brachial artery and moves it down the forearm and into the hands. The ulnar artery and veins are part of a common anatomical relationship called venae comitantes. While performing opposite functions, the two types of blood vessels are meant to complement each other's function.