Iliocostalis Lumborum

origin: anterior surface of a broad and thick tendon which originates
        from the sacrum, spinous proceses of the lumbar vertebrae and
        from the inner lip of the iliac crest;
insertion: inferior borders of the angles of the lower 6 or 7 ribs;
action: acting bilaterally, extension and hyperextension of the spine;
        acting unilaterally, laterally flexes the spine;
nerve supply: posterior rami of the spinal nerves;
synergists:   Longissimus Thoracis , Quadratus Lumborum;

Original Text by Clifford R. Wheeless, III, MD.