Overview
The atlas is the first cervical vertebra. As in other species it has no vertebral body and no spinous process: it is a ring made of a dorsal arch and a ventral arch, joined laterally by two masses from which the wings (alae atlantis) project. It articulates cranially with the occipital condyles and caudally with the axis. In cattle it is a robust bone with wide, thick wings.
Key features
- Cranial articular foveae: two deep cavities that receive the occipital condyles. The atlanto-occipital joint allows flexion and extension of the head (the "yes" movement).
- Caudal articular foveae: flatter surfaces for the axis. The atlantoaxial joint allows rotation of the head (the "no" movement).
- Fovea of the dens (fovea dentis): on the dorsal surface of the ventral arch, where the dens of the axis rests.
- Dorsal and ventral tubercles: small midline prominences on each arch.
- Wings of the atlas: wide and palpable on each side of the neck just caudal to the skull. On their ventral surface lies the atlantal fossa (fossa atlantis).
- Foramina: the lateral vertebral foramen (foramen vertebrale laterale), in the dorsal arch, and the alar foramen (foramen alare), in the wing, transmit the first cervical nerve and vessels. Unlike the dog, the cat and the horse, cattle have no transverse foramen.
Clinical relevance
- Cerebellomedullary cistern puncture: cerebrospinal fluid can be collected between the occipital bone and the dorsal arch of the atlas with the head flexed; the wings and the external occipital protuberance are the landmarks. In standing adult cattle the lumbosacral space is usually preferred.
- Congenital malformations of the occipitoatlantoaxial region: rare; described in calves with abnormal head posture and neurological deficits.
- Fractures and luxations: uncommon; they follow severe trauma.