The drawing shows the folds of mucous membrane, the vocal cords, which stretch from the tips of the arytenoid cartilages to the recess behind the median portion of the thyroid cartilage. To the outer side of each vocal cord is seen the thyro-arytenoid muscle (cut across), consisting of a broad outer portion, chiefly concerned in closing the glottis during the act of swallowing, and a smaller internal portion, which regulates the length and the thickness of the segment of the cord allowed to vibrate.