Vertebra. Coloured scanning electron micrograph (SEM) of a single vertebra, part of the vertebral column. It is composed of an anterior segment (top), called the vertebral body, which faces the chest, and a posterior segment (bottom), called the vertebral arch, which faces the back and encloses the vertebral foramen (hole in centre). When the vertebrae fit together, a semi-rigid, bony pillar is formed that supports the head, trunk and surrounding muscles. The vertebral foramina create a protected space, down which the spinal cord runs.