C1 and C2 bone anatomy

(A) Observe the occipital condyles that articulate with the superior articular surfaces (facets) of the atlas (vertebra C1).
(B) The atlas, on which the cranium rests, has neither a spinous process nor a body. It consists of two lateral masses connected by anterior and posterior arches.
(C, D) The tooth-like dens characterizes the axis (vertebra C2) and provides a pivot around which the atlas turns and carries the cranium. It articulates anteriorly with the anterior arch of the atlas ("Facet for dens" in part B) and posteriorly with the transverse ligament of the atlas (see part B).