Coccyx

The coccyx, commonly referred to as the tailbone, is the final group of vertebrae (the coccygeal vertebrae) below the sacrum. It is attached to the sacrum as a fibrocartilaginous joint, though there is not much movement here.

The coccyx is regarded as vestigial in humans, meaning it has no real use. It does provide an attachment for muscles, such as gluteus maximus[?], and also acts as a partial shock absorber when a person sits down.

The coccygeal bones fuse as a person ages. They can be damaged if a person sits down to quickly on a hard surface, causing a painful injury.