Coccyx

Recommended video: Sacrum and coccyx [08:45]

Bony structures and ligaments of the sacrum and coccyx.

The coccyx, otherwise known as the tailbone, is a small triangular shaped bone comprised of four fused coccygeal vertebrae. It marks the terminal point of the vertebral column and contributes to the formation of the walls of the true pelvis.

The coccyx consists of a base, apex, anterior surface, posterior surface and two lateral surfaces.

The base of the coccyx is located superiorly and articulates with the sacrum forming the sacrococcygeal joint. The apex of the coccyx is a distal rounded prominence that acts as an important attachment site for muscles and ligaments of the pelvic floor. The anterior surface is concave and is marked by a four grooves which represent the fusion of the coccygeal vertebrae. A vertical row of tubercles can be found along the posterior surface of the coccyx and are known as the coccygeal cornua. The coccygeal cornua of the 1st coccygeal vertebra (Co1) articulate with the sacral cornua to form a foramen for the transmission of the posterior division of the fifth sacral nerve. Rudimentary transverse processes can be found along the lateral surfaces of the coccyx. 

The coccyx functions as an important insertion site for multiple muscles, ligaments, and tendons. The gluteus maximus, levator ani and coccygeus muscles attach to the coccyx and provide support to surrounding structures. As well as being an important attachment site, the coccyx also functions in providing weight bearing support to a person in the seated position.