There are two atypical vertebrae in the cervical region: C1 (Atlas) and C2 (Axis).
C1 is named Atlas after the greek god who hold up the heavens. On its superior surface it has two superior articular facets that articulate with the occipital condyle. It forms a condylar synovial joint that allows for flexion and extension. Its inferior surface has two inferior articular facets that articulate with the superior articular facet of C2. Furthermore on the anterior side C1 has the anterior tubercle that contains a facet to articulate with the Dens of C2 to form a pivot synovial joint. This allows for rotation. There are no intervertebral discs between C1 and C2. Click here to see a model showing the atlanto-axial joint.
C1 is atypical because:
- No body
- No spinous process
C2 is atypical because:
- Extra knoblike structure (Dens)