The superior articular facets are concave, reniform facets located on the superior surface of each lateral mass that face superiorly and medially.  Each facet is narrowed in the middle (kidney-shaped) and occasionally completely divided into larger anterior and smaller posterior parts.  They articulate with the occipital condyles at the atlanto-occipital joints, thereby permitting flexion and extension of the head.  As with the lateral masses themselves, the long axes of the facets converge anteriorly.