Posterior atlantooccipital membrane

The posterior atlantooccipital membrane, broad but thin, is connected above, to the posterior margin of the foramen magnum; below, to the upper border of the posterior arch of the atlas. On either side this membrane is defective below, over the groove for the vertebral artery, and forms with this groove an opening for the entrance of the artery and the exit of the suboccipital nerve. The free border of the membrane, arching over the artery and nerve, is sometimes ossified. The membrane is in relation, behind, with the Recti capitis posteriores minores and Obliqui capitis superiores; in front, with the dura mater of the vertebral canal, to which it is intimately adherent.