Atlas Bone, Posterior View

Description

Seen from behind, the occipital bone frames the foramen magnum superior to the atlas (C1), with the posterior arch of C1 spanning transversely beneath the skull base. Lateral to the posterior tubercle, the sulcus arteriae vertebralis (groove for the vertebral artery) tracks across the superior surface of the posterior arch toward the transverse foramen, placing it posterior to the lateral masses and their superior articular facets. Inferior to C1, the axis (C2) aligns in the midline, its spinous process projecting posteriorly below the atlantoaxial joint. Lambdoid sutures and adjacent occipital landmarks provide cranial orientation. Posterior anatomy of the atlas matters because the vertebral artery and C1 nerve root traverse a confined corridor where bony variation can change risk during instrumentation. This is the view you want when teaching C1 lateral mass screw placement and posterior C1 ring anatomy, since the artery’s course over the posterior arch helps define safe trajectories and explains why a high-riding vertebral artery or an arcuate foramen can complicate fixation. It also clarifies the spatial relationship between the atlanto-occipital joint (flexion extension) and the atlantoaxial complex (rotation) in trauma patterns such as Jefferson fractures and atlantoaxial instability. Use this illustration in gross anatomy and neuroanatomy courses when introducing the craniovertebral junction, or in spine surgery texts discussing posterior C1 C2 fusion approaches and vertebral artery injury avoidance. It also suits radiology teaching files that correlate posterior bony landmarks with CT and CTA evaluation of the vertebral artery at the level of C1. Anatomical accuracy verified by SciePro's Medical Advisory Board.