The innermost pia mater is a highly vascular layer that is adherent to the surface of the spinal cord. Midway between the anterior and posterior roots the pia mater forms a flat continuous sheet, the denticulate ligament (eFig. 9.46B). At the posterior and anterior rootlets, sleevelike projections from the denticulate ligament extend out through the arachnoid mater to attach onto the dura mater. These delicate attachments anchor and position the spinal cord within the central area of the subarachnoid space.