The vertebral foramen (canal) at the lower lumbar levels is commonly trefoil in shape.   The foramen is enclosed anteriorly by the posterior surface of the vertebral body, by the pedicles laterally and by the laminae posteriorly.

The foramina contain the cauda equina (lumbar, sacral and coccygeal nerve roots), filum terminale and spinal meninges, spinal arteries and venous plexuses.