Insertion into an oval facet at the base of the dorsal surface of the great trochanter on its lateral side.
Relations.—Outer surface with the gluteus medius ([Fig. 90], b) and at the caudal border with the gemellus superior ([Fig. 163], 6). Inner surface with the capsularis and rectus femoris ([Fig. 92], b).
Action.—Rotates the femur so as to carry the foot out.
M. capsularis (gluteus quartus, or epimeralis).—The capsularis is a small flat bundle of muscle-fibres which lies obliquely beneath the gluteus minimus ([Fig. 163], 5) and gemellus superior (6) on the lateral or outer surface of the ilium.
Origin by fleshy fibres from the surface of the ilium over a triangular area between the origin of the rectus femoris ([Fig. 92], b) ventrad, the gemellus superior ([Fig. 163], 6) dorsad, and of the gluteus minimus ([Fig. 163], 5) craniad and the acetabulum caudad. The muscle passes over the smooth surface of the ilium and the pubis ventrad of the acetabulum and then over the capsule of the joint.
Insertion by fleshy fibres for about one centimeter in the middle line on the dorsal surface of the femur distad of the great trochanter.
Relations.—Outer surface with the gluteus minimus ([Fig. 163], 5), the gemellus superior (6), and the vastus lateralis ([Fig. 90], d). Inner surface with the ilium, the rectus femoris ([Fig. 92], b), the capsule of the joint, and the vastus medialis ([Fig. 92], c).
Action.—Rotates the thigh so as to carry the foot inward, hence antagonizes the iliopsoas.
M. gemellus inferior.—The gemellus inferior is a flat triangular muscle situated just caudad of the gemellus superior and beneath the obturator internus ([Fig. 90], e), so that it is seen on reflecting the latter
Origin from the dorsal one-half of the whole lateral surface of the ischium between the ischial spine and the ischial tuberosity. The fibres converge toward its insertion. The inner surface of the muscle is covered by a strong tendon.