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Dorsal carpal branch of radial artery - a small vessel which arises beneath the extensor tendons of the thumb, 1899. From 'The Treatise of the Human Anatomy and Its Applications to the Practice of Medicine and Surgery, Volume I' (1899). First dorsal metacarpal artery - arises just before the radial artery passes between the two heads of the first dorsal interosseous muscle and divides almost immediately into two branches which supply the adjacent sides of the thumb and index finger; the lateral side of the thumb receives a branch directly from the radial artery. (Photo by VintageMedStock/Getty Images)