The craniocervical junction is made up of the occipital bone, the first cervical vertebra (the atlas), and the second cervical vertebra (the axis). It protects the brain stem, spinal cord, and some of the cranial nerves. It is stabilized by the alar and cruciform ligaments, the anterior and posterior atlantooccipital membranes, the anterior longitudinal ligament, and the ligamentum flavum.