Atlas and axis

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Atlanto-occipital joint
Atlanto-axial joint

Atlas and axis basic anatomy

Illustration showing position of atlas and axis. Appreciate the transverse ligament and how this gives stability but allows rotational movement

View showing position of cruciform ligament relative to atlas, axis and skull base

Video explaining anatomy of the atlas and axis

Atlanto-occipital joint

The atlas takes part in the atlanto-occipital joint with the skull above and atlanto-axial joints with the axis below. These joints together permit free movement of the head.
The atlanto-occipital joint is a synovial joint formed between the occipital condyles of the skull and facets on the superior surface of the atlas (the facets can be seen in the images above). The primary movement allowed by this joint is flexion and extension (nodding).

Atlanto-axial joint

Consists of three joints formed between the axis and atlas. There are two lateral joints between the facets and a midline joint between the dens (odontoid peg) and the axis (the latter is sometimes considered two joints - one between where the bones of the peg and the axis make contact and the second between the peg and the transverse ligament). The primary function of this joint is to permit rotational movement of the head.