The air leaves the lungs through the trachea (windpipe), whichopens into the larynx (the voice-box, visible on the outside as theAdam's apple). The larynx is a valve consisting of an opening (theglottis) covered by two flaps of retractable muscular tissue called thevocal folds (they are also called "vocal cords" because of an earlyanatomist's error; they are not cords at all). The vocal folds can closeoff the glottis tightly, sealing the lungs. This is useful when we wantto stiffen our upper body, which is a floppy bag of air. Get up fromyour chair without using your arms; you will feel your larynx tighten.The larynx is also closed off in physiological functions like coughingand defecation. The grunt of the weightlifter or tennis player is areminder that we use the same organ to seal the lungs and to producesound.