Of the cervical vertebrae, the atlas (C1), axis (C2) and vertebra prominens (C7) are considered atypical cervical vertebrae.
The atlas (C1) lacks a body or spinous process. It has anterior and posterior arches with lateral masses. Its superior articular surfaces articulate with the occiput at the atlanto-occipital joint. This articulation contributes for than 50% of neck flexion and extension movement. Its inferior articular surfaces articulate with the axis at the atlanto-axial joint. The two lateral masses and anterior arch makes up its 3 ossification centers.
The axis (C2) is unique with an odontoid process (the dens) projecting from its superior surface. It has 5 ossification centers.
The vertebra prominens (C7) has the longest spinous process of all cervical vertebrae. It is also non-bifid. These features give rise to its name. Its transverse foramina are small and do not transmit the vertebral artery like the other cervical vertebrae.
For a basic anatomic description of the structure of a generic vertebra, see vertebrae.