Part 93

Origin.—The ventral surface of the ischium, just in front of the semimembranosus.

Insertion.—An oblique line on the posterior surface of the femur, near the lower part of the internal trochanter.

Action.—To extend the hip joint, and to adduct the thigh and rotate it outward.

Structure.—It is composed of parallel bundles of fibers directed downward, forward, and outward.

Relations.—Internally, the adductor, semimembranosus, and the obturator vessels; externally, the obturator externus and biceps femoris, the deep femoral artery, and the great sciatic nerve.

Blood-supply.—Deep femoral and obturator arteries.

Nerve-supply.—Great sciatic nerve.

2. =Obturator Externus= (Fig. 456).—This is a pyramidal muscle which extends across the back of the hip joint from the obturator foramen to the trochanteric fossa.

Origin.—The ventral surface of the pubis and ischium, and the margin of the obturator foramen.

Insertion.—The trochanteric fossa.

Action.—To adduct the thigh and to rotate it outward.

Structure.—It is almost entirely fleshy, the muscle-bundles being rather loosely connected. The insertion is pointed, flattened, and partly tendinous. The origin is perforated by the obturator vessels and nerve.

Relations.—Internally, the adductor and quadratus femoris and the deep femoral vessels; externally, the gemellus, the tendon of the obturator internus, the biceps femoris, and the great sciatic nerve; anteriorly, the hip joint, the pectineus, and the external pudic vein.

Blood-supply.—Deep femoral and obturator arteries.

Nerve-supply.—Obturator nerve.

3. =Obturator internus= (Fig. 451).—This arises by two heads within the pelvic cavity, the tendon emerging through the lesser sciatic foramen.

Origin.—(1) The pelvic surface of the pubis and ischium around the obturator foramen; (2) the pelvic surface of the shaft of the ilium and the wing of the sacrum.

Insertion.—The trochanteric fossa.

Action.—To rotate the femur outward.

Structure.—The ischio-pubic head lies on the pelvic floor and covers the obturator foramen. It is thin and fan-shaped. The iliac head extends along the lateral wall of the pelvis, and is pennate, with a central tendon throughout. Both terminate on a flat tendon which passes outward through the lesser sciatic foramen to be inserted into the trochanteric fossa. A synovial bursa facilitates the play of the tendon over the external border of the ischium.

Relations.—The pelvic surface is covered by the pelvic fascia and the peritoneum. The obturator vessels and nerve lie between the two heads, and the internal pudic vessels and nerve lie along the dorsal edge of the iliac head.

Blood-supply.—Obturator and internal pudic arteries.

Nerve-supply.—Great sciatic nerve.

4. =Gemellus= (Fig. 455).—This is a thin, triangular muscle, which extends from the external border of the ischium to the trochanteric fossa.

Origin.—The external border of the ischium near the ischiatic spine.

Insertion.—The trochanteric fossa.

Action.—To rotate the femur outward.

Structure.—Fleshy, some fibers being inserted into the tendon of the obturator internus.