Median Atlantoaxial Joint and Nearby Structures. Extensive soft tissue and bony resection has exposed the rostral vertebral canal and anterior surface of the posterior cranial fossa. A portion of the cranial dura as well as the tectorial membrane have been removed to demonstrate the clivus. Stumps of cranial nerves V, VI, VII, VIII, IX, X, XI, and XII are shown approaching their respective foramina of exit. The atlantic part of the vertebral artery is shown laying in grooves on the superior surface of the posterior arch of the atlas. The dens (odontoid process) is a bony projection from the body of the axis vertebra that extends superiorly into the vertebral foramen of the atlas. It is held firmly in place against the posterior surface of the anterior arch of the atlas by the transverse ligament of the atlas. This ligament attaches bilaterally to the medial aspect of the lateral masses of C1. A pair of strong alar ligaments connect the upper lateral edges of the dens to the corresponding margins of the foramen magnum adjacent to the occipital condyles. The alar and transverse ligaments serve as the principal stabilizers of the median atlantoaxial joint. Extending superiorly and inferiorly from the transverse ligament are, respective, superior and inferior longitudinal bands to the clivus and body of the axis. These bands are weak. These bands, with the transverse ligament, form the parts of the cruciate (or cruciform) ligament of the atlas. The spinal cord has been transected at the level of the third cervical segment. The dorsal rootlets of the C2 segment consolidated to form the dorsal root of the C2 spinal nerve. This root ends in a swelling, the dorsal root or spinal ganglion, near the intervertebral foramen. It joins the ventral root to form the definitive C2 spinal nerve. After exiting the intervertebral foramen it divides into dorsal and ventral primary rami (the latter not labeled). (Image courtesy of PA Rubino)