The coccyx

The coccyx(figure c) usually consists of four fused vertebrae forming a single piece or two pieces of bone, which mainly represent the bodies. The pelvic surface is concave and relatively smooth, while on the dorsal surface the rudimentary articular processes present as a row of tubercles. Superiorly the larger pair from the coccygeal cornua which articulate with the sacral cornua, and enclose the fifth sacral intervertebral foramen. The posterior wall of the vertebral canal of the coccyx is absent so that the sacral hiatus continues downwards over the back of the coccyx.