Zygapophyses

Zygapophyses are paired bony projections on the vertebrae that extend from the neural arch to articulate with adjacent vertebrae, forming part of the vertebral joints. They consist of superior zygapophyses (prezygapophyses) and inferior zygapophyses (postzygapophyses). The superior processes project upward to connect with the vertebra above, while the inferior processes project downward to connect with the vertebra below. The articulations, known as zygapophysial joints, are typically synovial and are covered by articular cartilage, with supporting joint capsules in many species.

Functionally, zygapophyses constrain movement of the spine and help stabilize the vertebral column. Their orientation varies by region: cervical vertebrae generally have facets that permit more rotation, thoracic vertebrae have facets oriented to limit sagittal flexion and to align with rib articulation, and lumbar vertebrae have more sagittally oriented facets that favor flexion and extension while restricting rotation. This arrangement distributes load and limits excessive motion to maintain spinal integrity.

In anatomy and paleontology, zygapophyses aid in identifying vertebrae and inferring locomotor capabilities and phylogenetic relationships. Their morphology and orientation reflect adaptations across different vertebrate groups and provide a key reference for comparative spinal anatomy.