The backbone, giving support to an animal and protecting the spinal cord. It is made up of a series of bones or vertebrae running from the skull to the tail with a central canal containing the nerve fibers of the spinal cord. In tetrapods the vertebrae show some specialization with the shape of the bones varying according to position. In the chest region the upper or thoracic vertebrae are shaped to form connections to the ribs. The backbone is only slightly flexible to give adequate rigidity to the animal structure.