obturator internus
The obturator internus muscle originates on the medial surface of the obturator membrane, the ischium near the membrane, and the rim of the pubis. It exits the pelvic cavity through the lesser sciatic foramen. The obturator internus is situated partly within the lesser pelvis, and partly at the back of the hip-joint. It functions to help laterally rotate extended thigh and abduct flexed thigh, as well as to steady the femoral head in the acetabulum.