This muscle is composed of two small bundles of fibres situated on the inner side of the thyroid cartilage, where they are separated from each other by the interposition of a pouch of mucous membrane (ventricle of the larynx).

Origin. - From the inner surface of the body of the thyroid cartilage.

Insertion. - By some of its fibres into the outer border of the arytenoid cartilage. Others mingle with those of the arytenoid muscle.

Action. - To constrict the larynx.