Axis: anatomy, location and function

Also called

C2

What it is

The second cervical vertebra (C2), distinguished by a tooth-like upward projection called the dens.

Location

Lies directly below the atlas (C1) and above C3.

Function

Forms a pivot on which the atlas and skull rotate, allowing head turning ('no' movement).

Body system

Skeletal · single, midline structure

FMA ID

FMA12520 (Foundational Model of Anatomy)

Key facts

• The dens (odontoid process) is held against the atlas by the transverse ligament and develops from the embryonic body of the atlas.
• It has a large bifid spinous process that is the first one palpable below the skull.
• There is no intervertebral disc between the atlas and axis.

Clinical relevance

A bilateral fracture through the pars interarticularis of C2 is called a hangman's fracture; fractures of the dens are also well known.

The nearest named structures in the 3D model, measured from the centre of each part:

• Atlas · skeletal
• Intervertebral disk of axis · skeletal
• Vertebral artery · cardiovascular
• Central canal of spinal cord · nervous
• Obliquus capitis inferior · muscular
• Third cervical vertebra · skeletal
• Anterior spinal artery · cardiovascular
• Superior oblique part of longus colli · muscular
• Medulla oblongata · nervous
• Rectus capitis posterior major · muscular