[1] It extends superoinferiorly between the body of the axis superiorly,[1] and (sources differ) the sacrum and possibly the coccyx[1] or upper sacral canal[2] inferiorly.

It is continuous with the tectorial membrane of atlanto-axial joint superiorly,[1][2] and with the deep dorsal sacrococcygeal ligament inferiorly.

In the thoracic and lumbar regions, it presents a series of dentations with intervening concave margins.

[citation needed] The posterior longitudinal ligament is generally quite wide and thin,[1] and has serrated edges.

[1][2] This ligament is composed of smooth, shining, longitudinal fibers - denser and more compact than those of the anterior longitudinal ligament - and consists of superficial layers occupying the interval between three or four vertebræ, and deeper layers which extend between adjacent vertebrae.