Final answer:
The feature of the second cervical vertebra is the dens or odontoid process, which is a bony projection that extends upward from the vertebral body.
Step-by-step explanation:
The second cervical (C2) vertebra, also known as the axis, has a distinctive feature called the dens or odontoid process. This is a bony projection that extends upward from the vertebral body. The dens articulates with the inner aspect of the anterior arch of the atlas, where it is held in place by the transverse ligament.