The anterior longitudinal ligament is a strong band supporting the anterior aspect of the vertebral column.  It is narrower superiorly (4-5mm) and broader inferiorly (20-25mm).  It extends from the anterior tubercle of C1 to the pelvic surface of the upper sacrum.  It is between 1-2mm thick and consists of three dense layers of collagen fibers.  The superficial layer extends over three or four vertebrae; the intermediate layer over two or three and the deep layer consists of laterally short fibers connecting adjacent vertebrae.  The fibers are strongly attached to the intervertebral margins, but loosely to the bodies.  Superiorly, the ligament is continuous with the anterior atlanto-occipital membrane.