The odontoid process is the most prominent structure. The synovial joint between the anterior arch of the atlas and the dens shows signs of slight degeneration. also the transverse portion of the cruciate ligament which holds the odontoid process posteriorly. The "transverse ligament" is covered by the rectorial membrane which constitutes a reinforcement of a parietal blade of the dura mater and which is continuous with the dura mater of the skull (pachymeninx). In addition, the thin apical ligament of the dens directly anchors the tip of the dens to the clivus portion of the foramen magnum. Posteriorly, the thin atlanto–occipital membrane connects the posterior arch of the atlas with the rim of the foramen magnum. The cisterna magna occupies the angle between the pons, the medulla oblongata, cerebellar tonsils and the posterior wall of the vertebral canal.