Iliococcygeus muscle

At a glance

English

Iliococcygeus muscle

Latin (TA2)

Musculus iliococcygeus

System

Muscle

Region

Trunk

Side

Paired, left and right

About the iliococcygeus muscle

Levator ani, the main muscle of the pelvic floor, is usually divided into three parts: puborectalis, pubococcygeus and iliococcygeus. Iliococcygeus is the most lateral and posterior of these. It is a thin, almost flat sheet that forms much of the back half of the pelvic floor, and in some people it is poorly developed or largely replaced by fibrous tissue.

Its fibres arise along a curved line on the inner wall of the pelvis. The front of this line is the hind end of levator ani's tendinous arch, a thickened band in the fascia covering obturator internus; behind, it reaches the ischial spine. From this long origin the fibres run backward and medially, meeting those of the opposite side in a midline seam, the anococcygeal body, and attaching to the sides of the lower coccyx. Coccygeus lies directly behind it, and pubococcygeus lies in front and medial to it. Above it lie the pelvic organs, separated by fascia; below it is the fat-filled ischioanal fossa.

Together with the other parts of levator ani and with coccygeus, it forms the pelvic diaphragm, a sling that supports the pelvic organs and resists the rise in abdominal pressure that comes with coughing, sneezing, lifting and straining. Its flat shape makes it more of a supporting shelf than a strong mover, but it helps to lift and tighten the floor and to keep the rectum and other organs in position. It is active at rest and contracts more strongly during effort.

The muscle is supplied by the nerve to levator ani, from the fourth sacral segment, which reaches its upper surface, and by branches of the pudendal nerve, especially the inferior rectal nerve, on its lower surface. Its blood comes from branches of the internal iliac artery, including the inferior gluteal and internal pudendal arteries. Weakness of the pelvic floor muscles can let pelvic organs sag downward, and pelvic floor training aims to strengthen them.

Attachments, action and supply

Origin

Ischial spine and the hind portion of the levator ani tendinous arch, on the obturator fascia.

Insertion

Anococcygeal body and the side of the lower coccyx.

Action

Supports the pelvic organs and raises and tightens the pelvic floor against rises in abdominal pressure.

Nerve supply

Nerve to levator ani (S4) and the inferior rectal branch of the pudendal nerve.

Blood supply

Branches of the internal iliac artery, including the inferior gluteal and internal pudendal arteries.