Atlas or C1 Cervical Vertebra, Lateral View

Description

Seen in lateral profile, the atlas (C1) forms a bony ring composed of anterior and posterior arches connected by bulky lateral masses. Superior and inferior articular facets occupy the lateral masses, with the superior facets facing superomedially to receive the occipital condyles and the inferior facets facing inferomedially toward C2. Broad transverse processes project laterally, each pierced by a transverse foramen for the vertebral artery. No vertebral body, no spinous process. Understanding C1 from the side matters because its architecture underpins the craniovertebral junction, where stability depends more on ligaments than on interlocking bony constraints. The transverse process and transverse foramen mark the vertebral artery’s course as it exits C2, enters C1, then sweeps posteriorly over the posterior arch in the vertebral artery groove, a relationship that drives safe trajectories during C1 lateral mass screw fixation. Lateral views also clarify the atlanto-occipital versus atlanto-axial joint surfaces, useful when teaching why Jefferson fractures follow axial loading and why atlanto-occipital dissociation is a separate, frequently fatal injury pattern. Use this illustration in gross anatomy and musculoskeletal modules when introducing the atlas as a ring vertebra and contrasting it with typical cervical vertebrae, or in radiology teaching alongside lateral cervical spine radiographs and CT bone windows. It also supports operative planning figures for posterior C1–C2 instrumentation, emphasizing the transverse process, lateral mass, and vertebral artery corridor. Anatomical accuracy verified by SciePro's Medical Advisory Board.