The axis (C2) is the second cervical vertebra. It has all the typical features of a vertebra. However, the body of the axis presents a specialized projection called dens that articulates with the atlas (C1) at the atlanto-axial joint. The movements provided by the joint include rotation of the head. Therefore, the dens is involved in head shaking when saying "no."

The features that are exclusively found on the axis include the following:

Dens (odontoid process) - a large tooth-like projection that extends superiorly from the vertebral body; it is held in place by the transverse ligament of the atlas that extends along its posterior aspect;
Apex of the dens - the highest point of the dens; serves as the attachment site for the apical ligament of dens;
Anterior articular facet - found on the anterior surface of the dens; articulates with the facet for dens situated on the anterior arch of the atlas;
Posterior articular facet - a smooth articular surface for the transverse ligament of the atlas; located on the posterior aspect of the dens;
Impression for alar ligament (2) - a shallow groove located on each upper aspect of the lateral side of the dens; serves as an attachment site for the alar ligament.

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Axis (C2)