Dorsal metacarpal veins are the three veins that are located on the back of the hand. These veins are made up of the dorsal digital veins, which are the veins that are located on adjacent sides of the second, third, and fourth fingers along the dorsal interossei. The dorsal interossei are muscles located between the metacarpals. The veins drain from the four fingers into the dorsal venous network in the hand. This network also consists of the dorsal digital vein from the radial side of the index finger and the veins of the thumb. Here the network moves upward and becomes the cephalic vein. The vein from the ulnar side of the little finger joins the network on the ulnar side and becomes the basilic vein. The dorsal metacarpal veins are deep veins that run parallel to the arteries and at some angles cross them. Valves are located in the veins that prevent the back flow of blood, ensuring that blood can only flow one way, and that oxygen-rich blood is always flowing through the hand. Medical personnel are able to draw blood from the dorsal metacarpal veins to perform diagnostic laboratory tests.