The coccyx commonly referred to as the tailbone, is the final segment of the vertebral column in humans and apes, and certain other mammals such as horses.

The coccyx is formed of either three, four or five rudimentary vertebrae. It articulates superiorly with the sacrum. In each of the first three segments may be traced a rudimentary body and articular and transverse processes; the last piece (sometimes the third) is a mere nodule of bone. The transverse processes are most prominent and noticeable on the first coccygeal segment. All the segments lack pedicles, laminae and spinous processes. The first is the largest; it resembles the lowest sacral vertebra, and often exists as a separate piece; the remaining ones diminish in size from above downward.