When movements in the sacrum increase the anteroposterior diameter of the pelvic outlet, movements in the sacrococcygeal joint can further increase this diameter.

It is known also as the base or root of the tail, and corresponds to the human sacrococcygeal symphysis.

The joint between the sacrum and the coccyx, the sacrococcygeal symphysis, is strengthened by a series of ligaments.

The coccyx is attached to the sacrum by a fibrocartilaginous joint, called the sacrococcygeal symphysis, allowing for some (but little) movement.

This short ligament forms the continuation of the anterior longitudinal ligament and stretches over the sacrococcygeal symphysis.

Together with the anterior, posterior, and intercornual sacrococcygeal ligaments, they stabilize the sacrococcygeal symphysis, i.e. the joint between the sacrum and the coccyx.

The posterior sacrococcygeal ligament or dorsal sacrococcygeal ligament is a ligament which stretches from the sacrum to the coccyx and thus dorsally across the sacrococcygeal symphysis shared by these two bones.

The sacrococcygeal symphysis (sacrococcygeal articulation, articulation of the sacrum and coccyx) is an amphiarthrodial joint, formed between the oval surface at the apex of the sacrum, and the base of the coccyx.

Comprising three to five separate or fused vertebrae (the coccygeal vertebrae) below the sacrum, it is attached to the sacrum by a fibrocartilaginous joint, the sacrococcygeal symphysis, which permits limited movement between the sacrum and the coccyx.