The larynx is protected above by a lid, a flexible, leaf-shaped cartilage, the epiglottis. The gullet, or food-passage to the stomach, is situated behind the larynx and windpipe, and the function of the epiglottis is to close the larynx and to act as a bridge over which food passes from the mouth into the gullet. But for the epiglottis, food might get into the larynx and thence into the windpipe every time we swallowed, with what distressing and even disastrous effect any one who has ever "swallowed the wrong way" well knows. When open, on the other hand, the epiglottis forms a beautifully smooth cartilaginous curve, over which the sounding air, the tone, as it issues from the larynx, is guided to the resonance cavities above the larynx, which are the cavities of the mouth and of the nose. While parts of these cavities are solid, like the roof of the mouth, other parts, like the soft palate, are pliable; while the tongue is so astoundingly mobile that it constantly can alter the resonance cavity of the mouth as to dimension and shape. The larynx is swathed and lined with membrane and muscle. These membranes and muscles are named after the cartilages to which they are attached, between which they lie, or which they operate. There is no reason why they should be enumerated now. The function of the muscles of the larynx is stated by all authorities with which I am familiar to be twofold--to open and close the glottis (the space between the vocal cords), and to regulate the tension of the vocal cords, because the vibrations of these are considered the determining factor of vocal pitch. Sir Morell Mackenzie, however, in describing the muscles of the larynx in a passage couched in untechnical language, unconsciously gives a hint of another purpose for which the complexity of muscles in the larynx may exist. After speaking of the "innumerable little fingers of the muscles which move the vocal cords," he continues: "These fingers (which prosaic anatomists call _fibres_), besides being almost countless in number, are arranged in so intricate a manner that every one who dissects them finds out something new, which, it is needless to say, is forthwith given to the world as an important discovery. It is probable that no amount of macerating or teasing ever will bring us to 'finality' in this matter; nor do I think it would profit us much as regards our knowledge of the physiology of the voice if the last fibrilla of tiny muscle were run to earth. The mind can form no clearer notions of the infinitely little than of the infinitely great, and the microscopic movements of these tiny strips of contractile tissue would be no more _real_ to us than the figures which express the rapidity of light and the vast stretches of astronomical time and distance. Moreover, no two persons have their laryngeal muscles arranged in precisely the same manner--a circumstance which of itself goes a considerable way toward explaining the almost infinite variety of human voices.