Coccyx

The coccyx (tailbone) is a bone or set of bones that makes up the lowest segment of the spinal column.

There are usually 4 or 5 small vertebra-like bones in the coccyx - the number varies between individuals and does not significantly alter the functionality. In addition to varying in the number of separate bones at birth, individuals vary in the way that the bones fuse together. The coccyx can fuse together to form a single bone structure - it can also form two or three distinct structures. In many cases, these structures are incompletely fused or nearly fused, making the number of bones a matter of perspective.