Atlas or C1 Cervical Vertebra, Inferior View

Description

Viewed from below, the atlas (C1) appears as a ring formed by the anterior and posterior arches joined to paired lateral masses. The inferior articular facets occupy the inferomedial surfaces of the lateral masses and face inferiorly to meet the superior articular facets of the axis (C2), bracketing the vertebral foramen centrally for the cervicomedullary junction. Anteriorly, the anterior arch sits opposite the posterior arch, and the transverse processes project laterally, framing the expected position of the transverse foramina. No vertebral body is present. This inferior perspective matters because it isolates the atlantoaxial joint surfaces that govern axial rotation and bear load transfer from the head to C2. Orthopaedic and neurosurgical planning for C1 lateral mass screws and C1 to C2 fusion depends on understanding the orientation of the inferior facets relative to the vertebral foramen and the transverse processes, which in turn approximates the course of the vertebral artery in the transverse foramen and along the superior surface of the posterior arch. Rheumatoid atlantoaxial instability and traumatic Jefferson fractures can distort these relationships. Small changes here have consequences. Use this artwork in gross anatomy and spine modules when teaching why C1 is a true ring vertebra and how the inferior facets couple with C2 to permit rotation while limiting translation. It also suits surgical textbooks and preoperative patient education materials discussing atlantoaxial fixation, facet alignment, and the risk corridors around the vertebral artery and spinal canal. Anatomical accuracy verified by SciePro's Medical Advisory Board.