The axis is the second of seven bones in the cervical spine, or the section of the vertebral column in the neck.

The axis, also known as the C2 bone, creates a pivot that allows the C1, or atlas, to rotate. This action gives the head and neck a greater range of motion from side to side. The pivoting motion occurs on part of the bone called the dens, a tooth-like upright section on the bone that. The dens in the axis is larger than any other vertebral bone.

Another special characteristic of the axis and all other cervical vertebrae is the absence of a body, or large flat portion of the bone. Because theses two bones lack this body, the neck has the largest range of motion of all the sections of the spinal column.

Injury to the atlas or axis, such as fracture from a high-impact collision or sudden, violent jerking of the head, can be fatal. The atlas and axis are the two most commonly injured cervical vertebrae bones.