The pudendal nerve, sciatic nerve, inferior gluteal nerve, and inferior gluteal artery all exit the sciatic foramen. The obturator nerve does not exit the sciatic foramen. The greater sciatic foramen is bounded as follows: anterolaterally by the greater sciatic notch of the illium, posteromedially by the sacrotuberous ligament, inferiorly by the sacrospinous ligament and ischial spine, and superiorly by the anterior sacroiliac ligament. It is partially filled up by the piriformis which leaves the pelvis through it. The following structures make their exit from the pelvis through the greater sciatic foramen above the piriformis: superior gluteal vessels and superior gluteal nerve. Below the piriformis the following structures exit: inferior gluteal vessels, inferior gluteal nerve, internal pudendal vessels, pudendal nerve, sciatic nerve, posterior femoral cutaneous nerve, nerve to obturator internus, and nerve to quadratus femoris. The obturator nerve originates from the L2, L3, and L4 nerve roots, exits the pelvis through the obturator foramen, innervates the gracilis, adductors (longus, brevis, magnus), and provides sensation to the inferomedial thigh.
Netter FH: Atlas of Human Anatomy. West Caldwell, NJ, CIBA-Geigy, 1989
Doty JR, Rengachary SS (eds): Surgical Disorders of the Sacrum. New York, NY, Thieme, 1994