Overview
The axis is the second cervical vertebra. Its body is long and extends cranially into the dens, the pivot around which the atlas rotates. It articulates cranially with the atlas and caudally with the third cervical vertebra.
Key features
- Dens: cranial projection of the body that rests in the fovea of the dens of the atlas, held by ligaments. In cattle, as in the horse, it is spout-shaped, concave dorsally, rather than peg-shaped as in the dog and cat.
- Cranial articular surfaces: on each side of the dens, for the caudal foveae of the atlas.
- Spinous process: long, shaped like a sagittal crest, thicker in its caudal part. Neck muscles such as the obliquus capitis caudalis originate on it.
- Transverse processes: small, directed caudally.
- Caudal articular processes and fossa of the body: articulate with the third cervical vertebra.
Clinical relevance
- Atlantoaxial joint: concentrates the rotation of the head; fractures of the dens and atlantoaxial luxations are rare in cattle and follow severe trauma.
- Vertebral osteomyelitis: in calves, blood-borne spread of bacteria can form abscesses in the vertebral bodies, including the cervical ones, with neck pain, stiffness and ataxia.
- Congenital malformations of the occipitoatlantoaxial region: rare; described in calves.