The obturator externus muscle covers the outer surface of the pelvis. The muscle is flat and fan-shaped.
It lies deep in the medial compartment of the thigh (the inner thigh) and is only visible when the pectineus muscle is reflected, or bent backward. The obturator externus muscle emerges from the margins of the obturator foramen, a space in the pelvic bones near the bottom of the pelvis, and the obturator membrane, which covers the foramen.
The fibers of the obturator externus muscle meet and course behind the neck of the femur, or thigh bone. It inserts into the trochanteric fossa of the femur, a depression in the bone’s neck.
The obturator externus muscle helps to steady the head of the femur in the acetabulum of the pelvis, the curved area where the thigh bone fits (at the hip). The obturator externus muscle also laterally rotates the thigh at the hip — as occurs in turning the leg so the feet point sideways — with the help of the gluteus maximus and medius muscles.