ORIGIN.--Approximately the anterior half attaches by an extensive aponeurosis, which is continuous anteriorly with that of M. extensor iliotibialis anticus, to the anterior iliac crest, ending posteriorly at the anterior end of the lateral iliac process; the posterior part attaches fleshily to the edge of the entire lateral iliac process and (posterior few mm.) aponeurotically to the entire lateral ischiatic ridge. The proximal part of the belly is much thicker than the fleshy origin. Two accessory aponeuroses associate with the anterior part of the muscle; the proximal one of these comes off the deep surface several mm. distal to the proximal end of the fleshy belly and passes medially between Mm. gluteus profundus and iliacus, fusing to both these muscles, and attaches to the lateral edge of M. iliotrochantericus medius and to the lateral edge of the ilium anterior to the latter; the aponeurosis actually splits into two sheets at the edge of M. iliotrochantericus medius; these sheets fuse to the dorsal and ventral surfaces of the latter muscle, enclosing it; the part of this aponeurosis between Mm. iliacus and iliotrochantericus medius is strongly fused with the underlying body wall. The distal accessory aponeurosis (sometimes weak) comes off the deep surface several mm. distal to the proximal one and passes medially along the ventral surface of M. iliacus, fusing with the latter, then joining the proximal accessory aponeurosis medial to M. iliacus. INSERTION.--The muscle inserts by a broad aponeurosis strongly fused to the underlying Mm. vastus lateralis and vastus medialis; the aponeurosis contributes superficially to the patellar tendon, attaching to the lateral half of the rotular crest. [Illustration: FIG. 16. _Tympanuchus pallidicinctus_ 2L. Lateral view of the muscles of the left leg. The following muscles, in addition to those listed for Fig. 14, have been removed: ambiens, vastus lateralis pars lateralis, vastus medialis (except for part of patellar tendon), extensor iliofibularis, flexor cruris lateralis (in part), flexor perforans et perforatus digiti II, and flexor perforans et perforatus digiti III. × 1.] INNERVATION.--A variable number of branches (usually two) of the middle division of the femoral nerve pass ventral to M. iliacus and between Mm. extensor iliotibialis anticus and vastus medialis and enter the deep surface of the anteroproximal part of the muscle. The branch of the middle peroneal division of the sciatic nerve emerges between the proximal ends of Mm. extensor iliofibularis and vastus lateralis and sends twigs into the deep surface of M. extensor iliotibialis lateralis. INDIVIDUAL VARIATION.--In two legs, the nerve supplying M. extensor iliotibialis anticus gives twigs into M. extensor iliotibialis lateralis. _T. cupido_ DIFFERENCES FROM _T. pallidicinctus_.--The fleshy origin from the lateral iliac process is considerably thicker (reflected in a thicker lateral iliac process).