GENERAL DESCRIPTION AND RELATIONS.--Small, thin, and triangular; lateral to antitrochanter and posterior part of trochanter; deep to M. extensor iliofibularis and posterior (adjacent) to M. gluteus profundus; distal half (or more) tendinous. ORIGIN.--The muscle arises fleshily from the posterior end of the anterior iliac crest (ventral to the origins of Mm. extensor iliotibialis lateralis and extensor iliofibularis) beginning adjacent to the posterior end of M. gluteus profundus. INSERTION.--The flat tendon narrows, overlaps the anteroproximal corner of insertion of M. flexor ischiofemoralis, and attaches to the lateral surface of the proximal part of the femur immediately anterior to the insertion of M. flexor ischiofemoralis and posterior to the proximal end of M. vastus lateralis; the attachment is posterodistal to the insertion of M. iliotrochantericus medius and posteroproximal to the insertion of M. iliacus. INNERVATION.--The small anterior peroneal division of the sciatic nerve turns anteriorly immediately after emerging from the ilio-ischiatic fenestra and passes deep to M. piriformis, giving twigs to the deep surface. INDIVIDUAL VARIATION.--In both legs of one specimen, the insertion does not overlap the insertion of M. flexor ischiofemoralis. The posteroproximal corner of the muscle is tendinous in one leg. _T. cupido_ INDIVIDUAL VARIATION.--The anterior border is somewhat fused with the posterior edge of M. gluteus profundus in one leg, while in another there is a slight gap between the origins of M. gluteus profundus and M. piriformis. In one leg, the posterior edge of the origin is aponeurotic. On both sides of one specimen, an accessory tendinous band arises several mm. posterior to the main part of M. piriformis and joins the proximal part of the insertional tendon, thus forming a Y-shaped unit (fig. 20I); the accessory tendon arises from the anterior end of the lateral iliac process (left side) or from the anterior part of the lateral iliac fossa (right side). The insertion may be proximal (rather than posterior) to the proximal end of M. vastus lateralis. In one leg, the insertional tendon is partly fused to the insertional tendon of M. flexor ischiofemoralis. _P. p. jamesi_ INDIVIDUAL VARIATION.--There is often a gap between the origins of M. gluteus profundus and M. piriformis. In one leg (fig. 20H), the posteroproximal corner of the muscle is aponeurotic. The insertion is often proximal (rather than posterior) to the proximal end of M. vastus lateralis. In one instance, the insertion does not overlap the insertion of M. flexor ischiofemoralis. =_M. Gluteus Profundus_= (M. iliotrochantericus posterior), Figs. 14, 16 _T. pallidicinctus_