The external surface is quadrilateral in shape. It is bounded above by a groove that lodges the tendon of the external obturator; below, it is continuous with the inferior ramus; in front it is limited by the posterior margin of the obturator foramen; behind, a prominent margin separates it from the posterior surface. In front of this margin the surface gives origin to the quadratus femoris, and anterior to this to some of the fibers of origin of the external obturator; the lower part of the surface gives origin to part of the adductor magnus.