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Each vertebra is attached to its neighbors not only by the intervertebral disks and the ligaments that we’ve seen, but also by the joints between the articular processes - the posterior joints. Each posterior joint is surrounded by a capsular ligament, which is loose enough to permit the small amount of movement that occurs between any two vertebrae.

The capsular ligament has no great strength, but the articular processes themselves are strong. Because the upper ones face forward and the lower ones backward, the articular processes prevent the vertebra above from slipping forward, relative to the vertebra below.