A flexible bony column in vertebrates that extends down the long axis of the body and provides the main skeletal support. It also encloses and protects the spinal cord and provides attachment for the muscles of the back. The vertebral column consists of a series of bones (see vertebra) separated by discs of cartilage (intervertebral discs). It articulates with the skull by means of the atlas vertebra, with the ribs at the thoracic vertebrae, and with the pelvic girdle at the sacrum (see sacral vertebrae).