The left and right lateral atlantoaxial joints are the articulations between the inferior articular surface of the lateral mass of atlas (C1) and the superior articular surface of the lateral mass of axis (C2). Since these are synovial joints, their articular surfaces are covered with hyaline cartilage.

The atlas and axis support the head on the lower cervical spine while providing for considerable mobility in flexion, extension, rotation and lateral bending. The first two vertebrae also function as conduits for the cervical cord and vertebral arteries.

The atlas (plural: atlases) is the first cervical vertebra, commonly called C1. It is an atypical cervical vertebra with unique features. It articulates with the dens of the axis and the occiput, respectively allowing rotation of the head, and flexion, extension and lateral flexion of the head.

atlanto-axial joint
The atlas and axis form the atlanto-axial joint, which allows head rotation. If you shake your head as if to say “no,” that is head rotation. The atlanto-axial joint is a compound synovial joint.

The atlas and axis are specialized to allow a greater range of motion than normal vertebrae. They are responsible for the nodding and rotation movements of the head. The atlanto-occipital joint allows the head to nod up and down on the vertebral column.

The atlas then fits on the axis (c-2) which has a projection up through the ring of the atlas called the dens. (fig. 1) This projection allows for stability and allows the neck to rotate around the axis. Inside of these two bones is the most important structure in the entire body, called the brain stem.

Atlas and axis vertebrae are two vertebrae in the vertebral column. Both are cervical vertebrae. They both are in the neck region. These two vertebrae are responsible for the motions of the head. Both vertebrae are ring-like bones.

The Atlas bone supports the weight of the skull, has facets that allow the head to move up and down and is responsible for the equilibrium management of the spine. The second neck bone is called Axis or C2 which is just below the Atlas bone, which allows the head to move from side to side.

The atlas is the top-most bone, sitting just below the skull; it is followed by the axis. Together, they support the skull, facilitate neck movement, and protect the spinal cord. (Think of them as BFFs—you won’t find one without the other.) Image from Human Anatomy Atlas.