The spine consists of the cervical, thoracic, lumbar and sacral vertebrae, of which there are seven cervical vertebrae, twelve thoracic vertebrae, five lumbar vertebrae, and a whole sacrum. The cervical, thoracic, lumbar and sacral form a complete spinal column. The spine has a physiological curvature, with the cervical vertebrae facing forward, the thoracic vertebrae facing backward, the lumbar vertebrae facing forward, and the sacral vertebrae facing backward. The bony structure consisting of the cervical, thoracic, lumbar, and sacral vertebrae contains a canal called the spinal canal, which houses the spinal cord and nerves. In the cervical and thoracic vertebrae is the spinal cord, and in the lumbar vertebrae is the cauda equina. The spine is composed of four parts: cervical, thoracic, lumbar, and sacral.