The atlas is the first cervical vertebra and the part of the spine closest to the skull. For this reason it bears the load of the entire skull. It is also called “nodding” because its structure and the muscles that attach to it enable nodding.
Due to its special position and its special function, the atlas, like the second cervical vertebra (axis), has a different structure than all other vertebral bodies. The atlas forms a functional unit with the axis and consists of a small anterior (ventral) and a large posterior (dorsal) vertebral arch. These vertebral arches each have a small bony attachment, the smaller tubercle anterius and the larger tubercle posterius.
On the inside of the anterior vertebral arch is a small pit, the fovea dentis. This serves as a joint connection to the second cervical vertebra, the dens axis. On each side there is a thickened bony structure, the lateral mass.
These have a concave articular surface at the top (Facies articularis superior), which serves as a joint connection to the occipital bone. Two further articular surfaces, the inferior articular facets, are located on the lower side of the lateral mass. These serve as the connection to the axis.
In the middle there is a large hole, the Foramen vertebrale. This serves the passage of the spinal cord. On each side there is a small bony protrusion, the Processus transversus.
In this there is a small hole, the Foramen transversarium. It leads the arteria vertebralis, which enters the head through the occipital hole (foramen magnum). The various bony protrusions serve as the origin and starting point for the prevertebral musculature and thus enable the head to move.
The atlas is the central element of the two head joints. On the one hand, it forms the atlantooccipital joint, which is the connection between the skull bone and the cervical spine. This joint enables flexion, extension and lateral movement of the head.
The atlantoaxial joint represents the articulated connection between the first and second cervical vertebrae. It enables the rotation of the head.