C1 vertebra

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The atlas is the most superior cervical vertebra. It supports the skull and is named after a character in Greek mythology who supported the earth on his shoulders. It exhibits little resemblance to other vertebrae:

  • ring-shaped
  • vertebral body is lost in development to the immediately inferior vertebra, the axis, where it forms the odontoid peg or dens
  • vertebral foramen:
    • more oval than the rest of cervical vertebrae
    • consists of anterior and posterior arches joined by lateral masses on each side
  • anterior arch:
    • shorter and straighter than posterior arch
    • connects lateral mass on each side to median anterior tubercle on its anterior surface
    • posterior to anterior tubercle on the surface of atlas facing vertebral canal is a facet for articulation with the dens of the axis
  • posterior arch represents pedicles and laminae of typical cervical vertebra:
    • connects lateral mass on each side to median posterior spinous tubercle; spinous process does not develop
    • close to lateral mass on superior surface is groove for vertebral artery as it passes to foramen magnum
  • lateral mass: junction of anterior and posterior arches
    • medial small tubercle for attachment to atlas ligament
    • has superior & inferior articular facets
  • superior articular facets:
    • articulate with condylar process of occipital bone
    • kidney-shaped and concave
  • inferior articular facets:
    • round and less concave than superior facets
    • articulate with axis
  • transverse process: broad, strong, occasionally bifid
    • represents posterior tubercle of other vertebrae
  • foramen transversarium: within the transverse process, it transmits vertebral vessels and sympathetic nerves

Last reviewed 01/2018

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