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The axial skeleton is divided into three sections: the skull, the vertebral_column (spinal_column), and the thorax.

The vertebral column extends from the skull to the pelvis, and creates a central support system for the body. The bones of the vertebral column are called the vertebrae (sing: vertebra). There are 24 single vertebral bones (7 cervical, 12 thoracic, and 5 lumbar), and 9 fused bones (the sacrum has 5; the coccyx has 4).

The vertebral column is flexible because of pads of fibrocartilage that lie between each bone. These pads are called intervertebral_discs. Each disc has a fluid center called the nucleus_pulposus and an outer ring of fibrous tissue called the annulus_fibrosus.

The basic structure of a vertebra consists of:

centrum (body),

vertebral_arch,

vertebral_foramen,

transverse_process,

spinous_process,

superior and inferior_articular_processes, and the

intervertebral_foramina.

C-1 is called the atlas bone, because it holds up the skull (like the legendary Atlas, who is reputed to have supported the world). C-1 lacks a centrum and its transverse processes have large concave depressions to support the skull.

C-2 is the axis bone and it acts as a pivot for the atlas. It has a large vertical process known as the odontoid_process (dens) that serves as the pivot point.

Anterior tubercle Posterior tubercle Transverse foramen Transverse process Transverse foramen Transverse process Superior articular facet of the lateral mass Superior articular facet of the lateral mass Superior articular facet of the lateral mass Anterior tubercle Posterior tubercle Transverse foramen Transverse foramen Transverse process Transverse process Inferior articular facet Inferior articular facet