6. Cervical spine radiograph, AP (open mouth) odontoid projection

For this projection the film cassette is placed behind the occiput, and the X-ray beam is aimed into the wide-open mouth. This provides optimal visualization of the dens, or odontoid process, of the axis.

Note how the ring shaped atlas casts two distinct parts to its shadow in this projection, referred to as the lateral masses of C1. Note the symmetrical arrangement of these lateral masses relative to both the body and dens of the axis.