The iliacus is a flat triangular muscle which covers the inner hollow surface of the iliac fossa. It originates from the inner aspect of the superior iliac crest, from the anterior and the iliolumbar ligaments, and from the sacrum, with insertion in lowermost surface of lesser trochanter of femur. It joins the psoas major to form the iliopsoas at the inguinal ligament. The iliacus muscle is supplied by the medial femoral circumflex artery and innervated by branches of the femoral nerve. It functions to flex and rotate the thigh laterally.