The structure indicated is the transverse foramen of a cervical vertebra.

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

Transverse foramina are only present in the cervical vertebrae. These foramina allow the passage of the vertebral artery and vein.

The vertebral arteries arise from the first part of the subclavian artery. The vertebral and internal carotid arteries provide the arterial supply to the brain, forming the Circle of Willis at the base of the brain.

After the vertebral artery is given off from the subclavian artery, it passes through the transverse foramina of cervical vertebrae C1 to C6. It then enters the skull via the foramen magnum.

Learn more about the anatomy of the vertebrae in this tutorial.