The structure indicated is the vertebral foramen.
There are 33 vertebrae which make up the spinal column:
- 7 cervical
- 12 thoracic
- 5 lumbar
- 5 fused sacral vertebrae
- 3-4 fused coccygeal vertebrae
The typical vertebra consists of the following features:
- Vertebral body
- Vertebral arch (neural arch) consisting of lamina and pedicle
- Spinous process
- Transverse process
- Vertebral foramen (collectively form vertebral canal)
- Superior and inferior articular processes
- Superior and inferior vertebral notches
The spinal cord passes through the vertebral foramina of the vertebrae: the collective vertebral foramina are referred to as the vertebral canal, or spinal canal. The anterior part of the vertebral foramen is formed from the posterior aspect of the vertebral body. The lateral and posterior parts of the foramen are formed by the vertebral (neural) arch, the pedicles and lamina respectively.
Learn more about the anatomy of the vertebrae in this tutorial.