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It arises from the spinous process of the ischium, and is inserted into the extremity of the sacrum; and into nearly the whole length of the os coccygis laterally. It retains the coccyx in place, and prevents it from being forced backwards during the evacuation of the faeces.

Origin: Spine of ischium, lesser sacrosciatic ligament. Insertion: Margin of coccyx, side of lower piece of sacrum. Nerve: Fourth sacral. Action: Raises and supports coccyx, forms back part of pelvic diaphragm.