The movable articulations of the skull comprise (1) the mandibular; and (2) those between the skull and the vertebral column, namely (a) between the occiput and atlas ; (b) between the atlas and epistropheus (axis) ; and (c) the ligaments which connect the occiput and epistropheus.

The union of the atlas and epistropheus is described in this section because, (1) there is often a direct communication between the synovial cavity of the trans- verse epistrophic and the occipito-atlantal joints; (2) the rotatory movements of the head take place around the dens (odontoid process) ; and (3) important liga- ments from the dens pass over the atlas to the occiput.