![]() ![]() Superior articular facets of the lateral masses can be divided into two parts, with the anterior part being larger and the posterior smallerĬentral or paramedian parts of the posterior arch can be absent and replaced by fibrous tissue Rectus capitis posterior minor: tubercle on the posterior arch of the atlasĪrcuate foramen: calcification of the posterior atlanto-occipital membrane Rectus capitis anterior: base of transverse processes Obliquus capitis inferior: transverse processes Obliquus capitis superior: transverse processes Levator scapulae: tip of the transverse processes At each lateral margin, there is a gap for the passage of the C1 nerve and vertebral artery, which sometimes ossifies and becomes a foramen. Innervated by C1. Posterior atlanto-occipital membrane: attached to upper border of the posterior arch to the outer margins of foramen magnum. Provides tertiary support against ventral translation of the dens.Īnterior atlanto-occipital membrane: attached to upper border of the anterior arch to the outer margins of foramen magnum Each end is attached to tubercles on the anterior arch of the atlas.Ītlantoaxial ligaments: attach from the lower border of the anterior arch of the atlas to front of the body of the axis. Transverse ligament: strong band that runs posterior to the dens of the axis, holding it in place. A capsule innervated by the C2 nerve surrounds the joint. ![]() Lateral atlantoaxial joint: hyaline-covered synovial joint between the inferior articular facet of the atlas and the superior articular facet of the axis which allows for the rotation of the head. The dens is held in place by the transverse ligament, with a bursa between the two. Median atlantoaxial joint: hyaline-covered synovial joint between the dens of the axis and the posterior aspect of the anterior arch of the atlas, allowing for the rotation of the head. ![]() Covered by a capsule and innervated by C1, this joint allows for flexion, extension and lateral flexion. Transverse foramina: contains the vertebral arteriesĪnterior tubercle: sometimes present on the anterior aspect of the transverse processĪtlanto-occipital joint: hyaline-covered synovial joint between the occipital condyle and concave facet of the lateral mass of the atlas. Longer than all of the transverse processes of the cervical vertebrae except C7 Medial surface: marked by vascular foramina and a tubercle for the attachment of the transverse ligament Inferior articular facet: circular, with a flat or slightly concave surface articulating with the lateral atlantoaxial joint Superior articular facet: kidney-shaped, concave and articulates with the occipital bone Inferior border: attachment for the posterior atlanto-axial membrane Superior border: attachment for the posterior atlanto-occipital membrane Superior surface: contains paired grooves for the C1 nerve and vertebral artery, sits just posterior to the lateral mass Posterior tubercle: sits on the posterior aspect of the posterior arch, is a rudimentary spinous process and attachment site for the ligamentum nuchae Lower border: attachment of the anterior atlanto-axial membrane and lateral parts of the anterior longitudinal ligament Upper border: attachment of the anterior atlanto-occipital membrane and lateral parts of the anterior longitudinal ligament ![]() Posterior facet for the dens: sits on the posterior aspect of the anterior arch The posterior 2/3 contains the spinal cord, which occupies 1/3 of the total vertebral canal space.Īnterior tubercle: sits on the anterior aspect of the anterior arch and is the site of attachment of the anterior longitudinal ligament The anterior 1/3 is occupied by the dens. The transverse ligament holds the dens of the axis against the anterior arch of the atlas and divides its vertebral canal into two parts. It does not have a vertebral body, instead the dens of the axis sit where a centrum (body) of a typical vertebra would be. The atlas is composed of an anterior arch and a posterior arch, paired lateral masses, and paired transverse processes. ![]()
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