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:
superior and inferior_articular_processes, and the
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.
The more typical cervical vertebrae (C-3 through C-7) are small, light, and have triangular vertebral_foramina. Their spinous process is short and often forks at the end. The spinous process of C-7 is visible through the skin and is called the vertebra_prominens. It is used as a reference point when counting vertebrae. Cervical vertebrae have wide transverse processes with foramina that accommodate the passage of the vertebral arteries (going towards the brain).