Bone: Axis (anatomy)
Second cervical vertebra, or epistropheus, from above.
Posterior atlantooccipital membrane and atlantoaxial ligament. (Axis visible at center.)
Gray's	subject #21 99

In anatomy, the second cervical vertebra (C2) of the spine is named the axis (from Latin axis, "axle") or epistropheus.

It forms the pivot upon which the first cervical vertebra (the atlas), which carries the head, rotates.

The most distinctive characteristic of this bone is the strong odontoid process ("dens") which rises perpendicularly from the upper surface of the body. That peculiar feature gives to the vertebra a rarely-used third name: vertebra dentata.

Contents 1 The body 2 Other features 3 Additional images 4 See also 5 External links

[edit] The body

The body is deeper in front than behind, and prolonged downward anteriorly so as to overlap the upper and front part of the third vertebra.

It presents in front a median longitudinal ridge, separating two lateral depressions for the attachment of the Longus colli muscles.

Its under surface is concave from before backward and convex from side to side.

[edit] Other features

The dens, or odontoid process, exhibits a slight constriction or neck where it joins the body.

The pedicles are broad and strong, especially in front, where they coalesce with the sides of the body and the root of the odontoid process. They are covered above by the superior articular surfaces.

The laminae are thick and strong, and the vertebral foramen large, but smaller than that of the atlas.

The transverse processes are very small, and each ends in a single tubercle; each is perforated by the transverse foramen, which is directed obliquely upward and laterally.

The superior articular surfaces are round, slightly convex, directed upward and laterally, and are supported on the body, pedicles, and transverse processes.

The inferior articular surfaces have the same direction as those of the other cervical vertebrae.

The superior vertebral notches are very shallow, and lie behind the articular processes; the inferior lie in front of the articular processes, as in the other cervical vertebrae.

The spinous process is large, very strong, deeply channelled on its under surface, and presents a bifid, tuberculated extremity.

[edit] Additional images

Median sagittal section through the occipital bone and first three cervical vertebræ.

Sagittal section of nose mouth, pharynx, and larynx.

[edit] See also

• Ossification of axis

[edit] External links

• Atlas of anatomy at UMich back_bone11 - "C2, 2nd Cervical Vertebra or Axis - Superior View"
• Atlas of anatomy at UMich back_bone12 - "C2, 2nd Cervical Vertebra or Axis - Posterior View"

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.

v • d • e Bones of torso (TA A02.2,3, GA 2.96-128) Sternum Suprasternal notch, Manubrium, Sternal angle, Body of sternum, Xiphisternal joint, Xiphoid process Rib specific ribs (1, 2, 9, 10, 11, 12, true – 1–7, false – 8–12, floating – 11–12) · parts (Angle, Tubercle, Costal groove, Neck, Head) Superior thoracic aperture · Inferior thoracic aperture · Intercostal space · Thoracic wall/Thoracic cage Vertebra General structures body of vertebra, vertebral arch (pedicle, lamina, vertebral notch), foramina (vertebral, intervertebral), processes (transverse, articular/zygapophysis, spinous), spinal canal Cervical vertebrae C1 (anterior arch, posterior arch, lateral mass), C2 (dens), C3, C4, C5, C6, C7 anterior tubercle, posterior tubercle, foramen transversarium Thoracic vertebrae T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12 costal facets (superior, inferior, transverse) Lumbar vertebrae accessory process, mammillary process, L5 Sacrum pelvic surface (anterior sacral foramina), dorsal surface (posterior sacral foramina, median sacral crest, medial sacral crest, lateral sacral crest), lateral surface (sacral tuberosity), base, sacral hiatus · presacral space · sacral promontory · sacral canal  · ala of sacrum · sacrovertebral angle Coccyx