The atlantooccipital joint is the articulation between the atlas and the occipital bone. It consists of a pair of condyloid joints. The ligaments connecting the bones are:
There are two synovial membranes: one lining each of the articular capsules. The joints frequently communicate with that between the posterior surface of the odontoid process and the transverse ligament of the atlas.
The movements permitted in this joint are (a) flexion and extension, which give rise to the ordinary forward and backward nodding of the head, and (b) slight lateral motion to one or other side. Flexion is produced mainly by the action of the Longi capitis and Recti capitis anteriores; extension by the Recti capitis posteriores major and minor, the Obliquus superior, the Semispinalis capitis, Splenius capitis, Sternocleidomastoideus, and upper fibers of the Trapezius. The Recti laterales are concerned in the lateral movement,assisted by the Trapezius, Splenius capitis, Semispinalis capitis, and the Sternocleidomastoideus of the same side, all acting together.