Final answer:
The axis vertebra, also known as the second cervical (C2) vertebra, enables head rotation side to side due to its dens, which articulates with the first cervical (C1) vertebra, the atlas. The correct option is 1) Axis vertebra
Step-by-step explanation:
The structure that furnishes the axis for the rotation of the head from side to side is the axis vertebra. The second cervical (C2) vertebra, known as the axis, is crucial for this rotary motion. Unlike any other vertebra, the axis has a distinctive bony projection called the dens (odontoid process), which extends upward from the vertebral body.
This den articulates with the atlas (C1 vertebra), providing a pivot around which the head turns. The atlas, being the first cervical vertebra, is a ring-shaped structure lacking a body or spinous process, with elongated transverse processes, and supports the skull.
The axis resembles other cervical vertebrae but can be identified by the dens, held in place by the transverse ligament, engaging with the anterior arch of the atlas. This articulation enables the side-to-side rotation of the head, facilitating movements such as turning to look right or left. The correct option is 1) Axis vertebra