Applied anatomy of the cervical spine

The atlas (Fig. 2) does not have a vertebral body – this has been absorbed into the axis vertebra, to form the odontoid process (Fig. 3). A thick anterior arch remains, extending into and joining the two lateral masses, on which are the superior atlantal joint facets, which articulate with the occipital condyles; and the inferior joint facets of the axis. The posterior arch is thinner than the anterior arch and forms the posterior junction of the lateral masses. The large vertebral foramen thus formed has a larger diameter in the transverse than in the sagittal plane. The transverse processes contain a transverse foramen through which the vertebral artery passes before it loops back above the upper surface of the posterior arch, which sometimes contains an arterial groove, although anatomical anomalies are frequently encountered. The posterior aspect of the anterior arch has a facet for articulation with the odontoid process of the axis, which is held in place by the transverse ligament, spanned between two tubercles, which project from the inner sides of the lateral masses.