The vertebra together make up the internal structure of the backbone, which supports the skull in the head. The vertebra have the spinal cord running throughout their lengths, branching out of each vertebra to help form the peripheral nervous sytem. The spinal cord and the brain inside the skull make up the main part of the nervous system, the central nervous system. There are 26 vertebra that comprise the main body of the backbone, and they start small in the neck and get progressively larger as they move down the curvature of the back. There are 7 cervical vertebrae in the neck, followed by 12 larger thoracic vertebra in the middle of the back. Finally, there are 5 large lumbar vertebra, located in the lower back. There is the sacrum, which is composed of 5 sacral bones, and the coccyx, which has 4 cocceal bones. The coccyx is the remainder of what would have been a tail, in prehistoric man. Each vertebra has a lubricated disc between it and the next vertebra to help absorb shock and prevent injury to the spinal cord.