Which of the following muscle of the larynx acts as abductor of vocal cords?

Posterior cricoarytenoid is the sole abductor of vocal cords. Therefore bilateral paralysis may lead to adduction of vocal cords and suffocation. They are called safety muscles of larynx. It arise from the posterior surface of lamina of cricoid on either side of midline, and is inseed on back of the muscular process of arytenoid cailage of its side. It acts on cricoarytenoid joint to rotate the arytenoid with its vocal process laterally so that muscular process turns posteriorly resulting in abduction of vocal cords and widening of rima glottis. Adductors of vocal cord: Lateral cricoarytenoid Transverse arytenoid