The basic unit of the vertebral column. Collectively, the vertebrae surround and protect the spinal cord and provide some type of axial support for the body. The stresses that the vertebral column must meet change somewhat from one end of the animal to the other, and also differ greatly between aquatic and terrestrial vertebrates because the problems of support and locomotion in these media are quite different. Accordingly, vertebral structure varies widely; yet all vertebrae have many features in common.