It is opened by the posterior cricoarytenoid muscles. It is bounded behind by the interarytenoid fold of the mucosa.
Moreover, The shape of the Rima glottidis changes with the movements of the vocal cords. It is the narrowest part of the larynx. The posterior cricoarytenoid muscle is the sole abductor of the true vocal folds, opening the rima glottidis by lateral rotation of the arytenoids and maximizing air passage during inspiration and expiration. These are the only muscles involved in abduction. They open the glottis by pulling the posterior ends of the arytenoid cartilages together.
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