Description: The obturator internus m. is a thick, fan-shaped muscle within the pelvis that covers the obturator foramen, attaching around its' perimeter, and to the thick obturator membrane. The obturator vessels and nerves lie on the surface of the m., exiting the true pelvis via the obturator canal. Sloping downward from antero-superiorly above, the muscle leaves the true pelvis by curving acutely around the ischium, below its' spine through the lesser sciatic foramen, to reach the greater trochanter of the femur.  Medial to the obturator internus m., the parietal pelvic fascia condenses between the pubis anteriorly, and the ischial spine to form the tendinous arch to which the levator m. of the pelvic floor are attached. Circulation reaches the m. from laterally via the superior gluteal a., and the nerve is from the sacral plexus (L5-S1).