Posterior view of the craniovertebral joints.  The postero-inferior aspect of the occipital bone is seen superiorly with the external occipital protuberance located in the midline. The occipital bone articulates with the atlas (C1 vertebra) via two atlanto-occipital joints formed between the occipital condyles and the superior articular facets of the atlas.  The superior articular facets are located on the lateral masses of C1.  The atlanto-occipital joints produce flexion and extension of the head.  The axis (C2 vertebra) articulates with the atlas at the atlanto-axial joint.  The atlanto-axial joint consists of three separate articulations.  Two lateral atlanto-axial joints are formed between the inferior articular facets of the atlas and the superior articular facets of the axis.  A third articulation, the median atlanto-axial joint is formed by the odontoid process of the axis and the anterior arch of the atlas.  The median atlanto-axial joint is a pivot joint that allows rotational movements of the head.  The vertebral artery is closely associated with the cranio-vertebral joints as it traverses the transverse processes of the cervical vertebrae before entering the skull via foramen magnum. (Image courtesy of AL Rhoton, Jr.)