Concept:The axis is the second cervical vertebra, recognized by a tooth-like projection called the odontoid process or dens.
This process allows rotation of the head.
Explanation:The diagram shows a vertebra with a peg-like upward projection from its body.
This projection is the odontoid process (dens), which is the characteristic feature of the axis vertebra.
The atlas is a ring-shaped vertebra with no odontoid process.
Ordinary cervical vertebrae and thoracic vertebrae also do not have this projection.
Since the dens is visible in the diagram, the illustrated part must be the axis bone.
The axis serves as a pivot that allows the atlas and skull to rotate from side to side.
Answer:B. axis vertebrae
