Coccygeus muscle

At a glance

English

Coccygeus muscle

Latin (TA2)

Musculus coccygeus

System

Muscle

Region

Trunk

Side

Paired, left and right

About the coccygeus muscle

Coccygeus forms the hindmost part of the muscular floor of the pelvis. It is a thin triangle of mixed muscle and tendon tissue, and in many people it is so fibrous that it can hardly be told apart from the ligament it lies on. Together with levator ani, which lies just in front of it, it completes the pelvic diaphragm, the hammock that closes the lower opening of the pelvis.

Its narrow apex is fixed to the ischial spine, the pointed projection on the back of the hip bone. From there it fans out medially and backward to a broad base on the lateral margin of the coccyx and the side of the lowest segment of the sacrum. Its outer (gluteal) surface is fused with the sacrospinous ligament, which runs along exactly the same line, and the muscle is often regarded as the muscular remnant of that ligament. Above and behind it lies piriformis; the gap between the two transmits nerves and vessels leaving the pelvis, and the pudendal nerve passes close to it on its way to the perineum.

The muscle helps to close the back part of the pelvic outlet and, with levator ani, to support the pelvic organs against downward pressure from the abdomen during coughing, straining and lifting. It also pulls the coccyx forward and steadies it, for example after it has been pushed backward during defaecation. In animals with a tail the equivalent muscle moves the tail to the side, which explains its position.

Coccygeus receives its nerve supply from the anterior rami of the fourth and fifth sacral nerves, which reach its pelvic surface directly. Its blood comes from small branches of the internal iliac artery. Spasm or tenderness in this muscle and its neighbours is one cause of pain around the coccyx, and it can be felt on internal examination just in front of the sacrospinous ligament.

Attachments, action and supply

Origin

Ischial spine and the adjoining part of the sacrospinous ligament.

Insertion

Lateral margin of the coccyx and the side of the lowest sacral segment.

Action

Supports the pelvic floor with levator ani and draws the coccyx forward, steadying it.

Nerve supply

Anterior rami of the fourth and fifth sacral nerves (S4, S5).

Blood supply

Branches of the internal iliac artery, chiefly the inferior gluteal artery.