Synonyms: C2, epistropheus, second cervical vertebra
Axis refers to the second cervical vertebra (C2), which together with the atlas forms the atlantoaxial joint.
The vertebral body of the axis vertebra is relatively large and dense in comparison with the other cervical vertebrae. The pediculi are broad and strong - especially anteriorly, where they converge on the dens axis. Above, they are covered with articular cartilage (superior articular facet). These joint surfaces are slightly convex and extend to the vertebral body, the pedicles and the transverse processes.
The laminae are also strong and thick. The vertebral foramen is broad, but slightly smaller than that of the atlas. The transverse processes are very small and end in a single tubercle. They each have a hole for the vertebral artery, the transverse foramen.
The most striking feature of the axis is a pronounced cone-shaped bony process, the dens, which articulates with the atlas. It extends - vertically and upwards - from the superior side of the vertebral body and tapers slightly at its origin. On its anterior surface there is a round to oval articulating facet that articulates with the anterior arch (arcus anterior) of the atlas. The back (posterior surface) shows a shallow depression that receives the transverse atlantal ligament. The tip of the dens provides attachment for the apical odontoid ligament. A little further towards the caudal zone the alaria ligaments are attached, which connect it to the occipital bone.
To comment on this article, please login..