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

Posterior Cricoarytenoid Muscle: The posterior cricoarytenoid muscle arises from the posterior aspect of the cricoid cailage and courses upward and laterally to attach to the muscular process of the arytenoid cailage. Its contraction pulls the muscular process backward and rotates the arytenoid cailage around a veical axis so that the two vocal processes are abducted and the size of the rima glottidis is increased.