The first cervical vertebra is called the atlas. It is the topmost of the seven cervical vertebrae and, therefore, the proximal one of the spinal column. Its vertebral foramen is aligned with the foramen magnum of the base of skull to allow the spinal cord to extend into the cranium as the medulla oblongata.
The first cervical vertebra looks differently from the rest of vertebrae as it lacks the spinous process on its posterior aspect. Rather, it is an irregular ring formed by two arches: the anterior and posterior arch. These are fused to one another by two thick lateral bone masses. On their superior surface, each of these masses bears an oval, concave superior articular facet, which is for the articulation with the occipital bone. Meanwhile, on their inferior surface, they have a flat inferior articular facet, which is for articulating with the superior surface of the second cervical vertebra (axis).
The 1st cervical vertebra anterior arch has an anterior tubercle and small facet for the odontoid process on the posterior surface which articulates with the dens of the axis. The atlas posterior arch has a posterior tubercle, which represents the missing spinous process (spine). Like the rest of the spinal column vertebrae, the atlas has two transverse processes, one on each lateral aspect of it, with an orifice in each one of them; they are for the vertebral arteries, which arise from the subclavian.
Below, the first cervical vertebra (superior aspect).
Below, inferior view of the atlas.
