The structure indicated is the gemellus inferior muscle.

The gemellus inferior muscle is one of the muscles of the gluteal region. The muscles in the gluteal region are divided into a superficial and deep group. There are four muscles of the superficial group:

1. Gluteus maximus
2. Gluteus medius
3. Gluteus minimus
4. Tensor fasciae latae

There are 5 muscles in the deep group:

1. Gemellus superior
2. Gemellus inferior
3. Quadratus femoris
4. Piriformis
5. Obturator internus

The word gemellus comes from the Latin “gemelli” which means “twins”. There are therefore two gemelli muscles, the gemellus superior, and the gemellus inferior. The gemelli muscles are located either side of the obturator internus tendons. The gemellus inferior is located inferior to the obturator internus tendon and its fibres blends with the inferior aspect of the tendon. The gemellus superior is located above the tendon and its lower fibres blend with the upper aspect of the obturator internus tendon.

Origin: posterior ischial tuberosity and postero-lateral obturator ring

Insertion: medial surface of greater trochanter of femur

Action: lateral rotation of hip. Assists abduction of hip when hip is flexed.

Innervation: nerve to quadratus femoris

Learn more about the anatomy of the gluteal muscles in this tutorial.