Atlas

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