The posterior part of the arch presents above and behind a rounded edge for the attachment of the posterior atlantooccipital membrane, while immediately behind each superior articular process is a groove (sulcus arteriae vertebralis), sometimes converted into a foramen by a delicate bony spiculum which arches backward from the posterior end of the superior articular process. The diminutive size of this process prevents any interference with the movements between the atlas and the skull. It ends behind in the posterior tubercle, which is the rudiment of a spinous process and gives origin to the Recti capitis posteriores minores and the ligamentum nuchae. The posterior arch forms about two-fifths of the circumference of the ring. The upper and lower borders respectively give attachment to the anterior atlantooccipital membrane and the anterior atlantoaxial ligament the former connects it with the occipital bone above, and the latter with the axis below.

Posteriorly it is concave, and marked by a smooth, oval or circular facet (fovea dentis), for articulation with the odontoid process (dens) of the axis. Its anterior surface is convex, and presents at its center the anterior tubercle for the attachment of the Longus colli muscles and the anterior longitudinal ligament. The anterior arch forms about one-fifth of the ring. It articulates with the Occiput above and C2 (the Axis) below. It is comprised of two bony arches with two bony masses laterally.

The Atlas (the first cervical vertebra - C1) differs from the other cervical vertebrae in that it has no body or spinous process.

Atlas bone