Superior transverse view of spinal cord and canal at atlantooccipital junction. The cervical spine has been separated from the skull and the large superior articular facets that articulate with the occipital condyles are in view. The remainder of the atlas consists of anterior and posterior arches with their respective tubercles, lateral masses containing the articular processes, and the transverse processes containing foramina for the vertebral arteries. Posterior to the anterior arch is the dens of the axis (C2 vertebra), which is firmly held against the arch by the strong transverse ligament of the atlas. Within the vertebral canal is the cross-section of the spinal cord, paired dorsal (posterior) and ventral (anterior) spinal nerve roots, and atlantic part of the vertebral arteries. (Image courtesy of PA Rubino)