coxis

Coxis is a term occasionally encountered in anatomical literature, but in modern English anatomy the term coccyx is preferred. When used, it refers to the coccyx, the small terminal segment of the vertebral column at the base of the spine.

The coccyx typically consists of three to five rudimentary vertebrae that are fused in adulthood. It articulates superiorly with the sacrum at the sacrococcygeal joint and is connected to the surrounding ligaments and muscles that form the pelvic floor.

Its functional role is largely as a site of attachment for ligaments and for muscles such as the coccygeus and parts of the levator ani complex, contributing modestly to the support of pelvic organs and to the mechanics of sitting.

Clinically, pain localized to this region is known as coccydynia. It can follow falls, prolonged sitting, childbirth, or degenerative changes. Management is usually conservative and includes cushions, nonsteroidal anti-inflammatory drugs, physical therapy, and, rarely, injections or surgery for refractory cases.

Origin of the term coccyx stems from the Greek kokkyx, meaning cuckoo, alluding to its beak-like shape. The term coxis is not widely used in contemporary anatomy and can be confused with os coxae, the hip bone.

The coccyx is a vestigial element of the tail; in humans it has limited motion and is generally fused, reflecting evolutionary reduction of tails.