"When the lungs are filled by a deep inspiration and the breath is held, the glottis is of necessity closed so tightly that no air can escape. In this condition the expiratory muscles may be very violently contracted, and still no air will escape; indeed, the greater the strength exerted the tighter is the closure of the glottis. Obviously, this closure of the glottis cannot be effected by the contraction of the glottis-closing muscles, strictly speaking, for these muscles are too small and weak to withstand the powerful air pressure exerted against the vocal cords.[4] The point of resistance is located just above the vocal cords. The sudden air pressure exerted on the interior walls of the larynx by the expiratory contraction causes the ventricles of the larynx to expand by inflation. This inflation of the ventricles brings their upper margins, formed by the false vocal cords, into contact. Thus the opening from the larynx into the pharynx is closed. This closure is not effected by any muscular contraction, therefore it is not dependent on the strength of the muscular fibers of the false vocal cords. It is an automatic valvular action, directly under voluntary control so far as the contraction of the expiratory muscles is concerned, but independent of volition as regards the action of the false vocal cords. On account of their important function in this operation the false vocal cords are called the 'breath-bands.' Closure of the glottis by the inflation of the ventricles imposes no strain on the vocal cords. [Note 4: One of the strongest arguments of the "breath-band" advocates is based on this action,--the resistance of the closed glottis to a powerful expiratory pressure. The theory of breath-control by "opposed muscular action" takes no cognizance of this operation. It will however be shown in Chapter II of Part II that the "breath-band" theorists are mistaken in asserting that the action of holding the breath is not performed by the glottis-closing muscles.]