The Atlas is the first cervical vertebra (C1). This thin ring shaped bone has no body and consists of an anterior and a posterior arch. It articulates with the Occipital bone on the base of the skull above and the Axis (C2) below. The Atlas supports the head and rotates on the facets of the Axis. Unlike the other vertebrae, it contains a transverse foramen through which the vertebral arteries and veins pass. The Atlas contains spinal nerve roots in narrow intervertebral foramen which risk compression.