Abductor of vocal cord is

The posterior cricoarytenoids are the only intrinsic muscles of the larynx which abduct the vocal cords to allow entry of air through rima glottidis to the respiratory tract below. When posterior cricoarytenoids contract muscular processes of both carotenoids rotate medially. As a result, vocal processes rotate laterally. i.e. abducting vocal cords and providing wide diamond shaped opening of the glottis. If they are paralyzed the adductor muscles of the larynx take the upper hand and the person might die due to the lack of air. Hence, the posterior cricoarytenoids are called safety muscles of the larynx.Cricothyroid tenses the vocal cords.Lateral cricoarytenoid adducts the vocal cords.Thyroarytenoid relaxes the vocal cords.Reference: Textbook of anatomy, Head neck, and brain, Vishram Singh, 2nd edition, page no.224