Odontoid peg

In anatomy, the second cervical vertebra (C2) of the spine is named the axis (from Latin axis, 'axle') or epistropheus.A fracture of the base of the dens as seen on plain X rayA fracture of the base of the dens as seen on CTType 3 odontoid fractureType 2 dens fractureIts shape and position (shown in red) from above. The skull is shown in semi-transparent.Axis seen from above.3D imagePosterior atlantooccipital membrane and atlantoaxial ligament. (Axis visible at center.)Median sagittal section through the occipital bone and first three cervical vertebræ.Sagittal section of nose mouth, pharynx, and larynx.Axis on x-rayUnfused arch of atlas at CT. In anatomy, the second cervical vertebra (C2) of the spine is named the axis (from Latin axis, 'axle') or epistropheus. By the atlanto-axial joint, 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 known as the 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. In some judicial hangings the odontoid process may break and hit the medulla oblongata, causing death.