Axial skeleton · Vertebral column
Axis (C2)
The axis is the second cervical vertebra. Its dens projects up into the ring of the atlas and forms the pivot about which the atlas, carrying the skull, rotates.
- Latin (TA)
- Axis
- Type
- Irregular bone: an atypical cervical vertebra recognised by the tooth-like dens projecting up from its body
- Side
- Midline — single
- Model size
- 5.4 cm longest
Rotate the bone to inspect every surface. Blue dots are landmarks — tap one.
3D model: Z-Anatomy (CC BY-SA 4.0), derived from BodyParts3D © DBCLS (CC BY-SA 2.1 JP). Adapted by PharmaWallah. Credits & licence
Landmarks
4 of 10 marked on the modelTap a landmark to find it on the bone and read what it is.
A strong, tooth-like process projecting upwards from the body of the axis.
Where: Upper surface of the body, in the midline.
Why it matters: The pivot of the median atlanto-axial joint. Developmentally it represents the body of the atlas, which fused with the axis.
Related: Median atlanto-axial joint; transverse, alar and apical ligaments.
Viva: What does the dens represent developmentally?
Marked on the model at the point Z-Anatomy places this label.
The pointed upper tip of the dens.
Where: Top of the dens.
Why it matters: Attachment of the apical ligament, which runs up to the anterior margin of the foramen magnum.
Related: Apical ligament of dens.
Marked on the model at the point Z-Anatomy places this label.
An oval smooth facet on the front of the dens.
Where: Anterior surface of the dens.
Why it matters: Articulates with the facet for the dens on the anterior arch of the atlas.
Related: Median atlanto-axial joint.
Marked on the model at the point Z-Anatomy places this label.
A smooth surface on the back of the dens.
Where: Posterior surface of the dens, near its base.
Why it matters: Articulates with the transverse ligament of the atlas, which holds the dens forwards against the anterior arch.
Related: Transverse ligament of atlas.
Viva: What articulates with the posterior facet of the dens?
Marked on the model at the point Z-Anatomy places this label.
The block of bone below the dens.
Where: Anterior part of the axis, below the dens.
Why it matters: Its lower surface is joined to the body of C3 by the highest intervertebral disc; the tectorial membrane, the upward continuation of the posterior longitudinal ligament, attaches to its posterior surface.
A large, flat, oval articular surface on each side of the dens.
Where: Upper surface of the body and pedicle on each side, facing upwards and laterally.
Why it matters: Articulates with the inferior articular surface of the atlas at the lateral atlanto-axial joint.
Related: Lateral atlanto-axial joint.
A downward projection at the junction of pedicle and lamina, with a facet facing downwards and forwards.
Where: Below each lamina, behind the line of the superior facets.
Why it matters: Forms a zygapophysial joint with C3, like a typical cervical vertebra.
Related: Zygapophysial joint (C2–C3).
A large, strong, bifid spinous process.
Where: Posterior midline of the vertebral arch.
Why it matters: The first spinous process you can feel below the back of the skull in the midline of the neck; it gives attachment to suboccipital muscles and the ligamentum nuchae.
Related: Rectus capitis posterior major; obliquus capitis inferior.
Viva: Which suboccipital muscles arise from the spinous process of the axis?
Classification & region
Irregular bone: an atypical cervical vertebra recognised by the tooth-like dens projecting up from its body.
- Dens (odontoid process)
- The peg that projects upwards from the body and acts as the pivot around which the atlas turns.
- Body
- Below the dens; joined to the third cervical vertebra by the first intervertebral disc.
- Vertebral arch
- Thick pedicles and laminae ending in a large, bifid spinous process.
- Processes
- Large superior articular facets beside the dens, typical inferior articular processes, and small transverse processes with foramina transversaria.
Hold it in the anatomical position
- The dens points upwards.
- The body and dens are in front; the large bifid spinous process points backwards.
- The large, flat superior articular facets lie on either side of the dens and face upwards (and laterally).
- The inferior articular processes lie further back, below the laminae, and face downwards and forwards like those of a typical cervical vertebra.
Orientation (a midline bone has no side)
- Superior vs inferior: the dens projects upwards.
- Anterior vs posterior: the dens carries an oval articular facet on its front (for the atlas); the large spinous process points backwards.
- Check that the superior articular facets sit beside the dens, in front of the line of the inferior articular processes.
The axis is a single midline bone with symmetrical halves, so it has no side; you orient it instead.
Articulations
- With the atlas (anterior arch) at the Median atlanto-axial joint, synovial pivot joint — Anterior articular facet of the dens (the posterior facet meets the transverse ligament)..
- With the atlas (lateral masses) at the Lateral atlanto-axial joint, synovial plane joint — Superior articular facets..
- With the third cervical vertebra (body) at the Intervertebral disc joint (symphysis), the highest disc in the column — Inferior surface of the body..
- With the third cervical vertebra (articular processes) at the Zygapophysial joint, synovial plane joint — Inferior articular facets..
Muscle and ligament attachments
| Structure | Type | Where on the bone |
|---|---|---|
| Apical ligament of the dens | ligament | Apex of the dens. |
| Alar ligaments | ligament | Sides of the upper part of the dens (running to the occipital condyles). |
| Tectorial membrane | ligament | Posterior surface of the body. |
| Anterior longitudinal ligament | ligament | Anterior surface of the body. |
| Ligamentum nuchae | ligament | Spinous process. |
| Rectus capitis posterior major | origin | Spinous process. |
| Obliquus capitis inferior | origin | Spinous process. |
| Semispinalis cervicis | insertion | Spinous process. |
Functions
- Provides the pivot (the dens) around which the atlas and skull rotate.
- Transfers the weight of the head from the atlas to the rest of the cervical column.
- Gives strong attachment to the suboccipital muscles and the ligaments that stabilise the head on the neck.
Clinical & practical relevance
- Fractures of the dens can follow falls or road accidents; an unstable fracture threatens the spinal cord and brainstem.
- Hangman's fracture is a fracture through the bony arch of the axis between its superior and inferior articular processes, caused by severe hyperextension of the neck.
Identification tips
- Dens up = axis. No other vertebra has a peg on top.
- The axis's superior facets sit in front of its inferior facets, unlike the stacked pillars of other cervical vertebrae.
- Anterior facet meets bone (atlas); posterior facet meets ligament (transverse).
Common student mistakes
- Saying the dens is part of the atlas: it belongs to the axis, though it develops from the atlas's body.
- Thinking the alar ligaments go to the foramen magnum: they run to the occipital condyles; the apical ligament goes to the foramen magnum.
- Placing a disc between atlas and axis.
Common exam questions
How do you identify the axis?Show answer
By the dens projecting upwards from its body, large superior articular facets beside it, and a large bifid spinous process.
What are the articular facets on the dens and what do they meet?Show answer
An anterior facet that meets the anterior arch of the atlas and a posterior facet that meets the transverse ligament of the atlas.
Name the ligaments attached to the dens.Show answer
The apical ligament at the apex and the alar ligaments on its sides; the transverse ligament passes behind it.
Where is the first intervertebral disc?Show answer
Between the bodies of the axis and C3; there is no disc between skull and atlas or between atlas and axis.
Which movement occurs at the atlanto-axial joints?Show answer
Rotation of the head (shaking the head 'no').
What is a hangman's fracture?Show answer
A fracture through the bony arch of C2 between its articular processes, from forceful hyperextension.
Revision summary
- C2 is recognised by the dens.
- Dens: anterior facet (atlas) and posterior facet (transverse ligament).
- Apical ligament from the apex; alar ligaments from the sides.
- Large superior articular facets for the lateral atlanto-axial joints.
- First intervertebral disc is between C2 and C3.
- Large bifid spinous process: origin of rectus capitis posterior major and obliquus capitis inferior.
Test yourself on the axis (c2)
Spotting questions on bones, sides and landmarks — untimed, with explanations.
References
- Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. 5th ed. Philadelphia: Elsevier; 2023.
- Moore KL, Dalley AF, Agur AMR. Moore's Clinically Oriented Anatomy. 9th ed. Philadelphia: Wolters Kluwer; 2023.
- Federative International Programme for Anatomical Terminology (FIPAT). Terminologia Anatomica. 2nd ed. FIPAT.library.dal.ca; 2019. fipat.library.dal.ca/TA2
- Kervyn G, Zielinski M, Vinent L, et al. Z-Anatomy: the libre 3D atlas of anatomy. Models derived from BodyParts3D, The Database Center for Life Science (CC BY-SA 2.1 JP). CC BY-SA 4.0. www.z-anatomy.com/
Prepared by the PharmaWallah student team. Verify results with your textbook or instructor. Report an error · Editorial policy