Concept:The odontoid process is a peg-like projection found only on the axis vertebra.
Explanation:The vertebral column is divided into cervical, thoracic, lumbar, sacral, and coccygeal vertebrae.
The odontoid process is also called the dens.
The atlas is the first cervical vertebra (
C1).
The axis is the second cervical vertebra (
C2).
The odontoid process projects upward from the body of the axis.
The atlas is ring-like and has no body, so the dens fits into it to form the atlanto-axial joint.
This joint permits rotation of the head from side to side.
Because the odontoid process arises only from the axis, it is not present on the atlas, the thoracic vertebrae, or the sacral vertebrae.
Answer:Option A: axis vertebra.