iliacus /ilī″əkəs/ [L, ilium, flank] , a flat triangular muscle that covers the inner curved surface of the iliac fossa. It arises from the inner aspect of the superior iliac crest, from the anterior and the iliolumbar ligaments, and from the sacrum. It joins the psoas major to form the iliopsoas at the inguinal ligament. The iliacus is innervated by branches of the femoral nerve that contain fibers from the second and third lumbar nerves. It acts to flex and laterally rotate the thigh. Compare psoas major, psoas minor.
