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 (sacrum has 5; 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

There are twelve thoracic vertebrae (T-1 through T-12), and they are distinguished by their distinctive heart-shaped centrum, which has costal_demifacets (one superior and one inferior) for the attachment of ribs.

They also have long spinous processes and an oval or round vertebral foramen. Their transverse processes have articular_facets that connect with the tubercles of the ribs.