When the spinal vertebrae are articulate with each other the bodies form a strong pillar for the support of the head and trunk, and the vertebral foramina constitute a canal for the protection of the medulla spinalis (spinal cord). Between every pair of vertebræ are two apertures, the intervertebral foramina (singular: foramen; also called neural foramina). The foramen allows for the passage of the spinal nerve root, dorsal root ganglion, the spinal artery of the segmental artery, communicating veins between the internal and external plexuses, recurrent meningeal (sinu-vertebral) nerves, and transforaminal ligaments.