In some people, the fibres of the gemellus superior extend further than average, and are prolonged onto the medial surface of the greater trochanter of the femur.[2] The inferior gemellus muscle arises from the upper part of the ischial tuberosity, immediately below the groove for the internal obturator tendon.It blends with the lower part of the tendon, and is inserted with it into the medial surface of the greater trochanter.[1] The gemelli muscles act to compensate the reduced power of the internal obturator as it turns around the lesser sciatic notch.[2] Gemellus is the diminutive of "geminus"[clarification needed] meaning twin, doubled or duplicated.