The larynx is a sound-giving organ belonging to that class of wind instruments called reed instruments, although it differs in various respects from all artificial arrangements of the kind. The sound or tone-generating apparatus of the larynx consists of tense, elastic _membranes_, the so-called _chordæ vocales_, which are enclosed in a sounding case composed of movable cartilaginous plates, and may be stretched by a certain apparatus of muscles in very different and exactly measurable degrees. They are made to vibrate audibly by a current of air impelled with various degrees of force and at will by the lungs in expiration through the narrow chink (glottis) formed by the fine edges of the chords. Thus the lungs correspond to the bellows of the organ; the trachea, at the top of which the vocal instrument is placed, answers to the conduit (_Windrohr_), and the cavity of the throat in front of the instrument with its two avenues, the mouth and the nostrils, to the resonance pipe (_Ansatzrohr_). THE LUNGS The lungs are two cellular, sponge-like elastic organs, largely made up of little cavities of conical shape, which, in the regular alternations of two opposite respiratory movements of air, are at one time expanded, and then again compressed. The two lungs are not of equal size; the right lung is one-tenth larger in volume than the left. THE TRACHEA, OR WINDPIPE, Through which the air of the lungs enters and passes out, consists of from sixteen to twenty-six cartilaginous rings, posteriorly incomplete, lying horizontally one above the other. These rings are connected by a membrane covering them externally and internally. As they enter the cavity of the chest, they divide into two branches, likewise composed of rings, one entering the right, the other the left lung. Before they join the lungs they divide again into several smaller branches, which again subdivide fork-like in the lungs, and terminate in numberless little grape-like clusters of hollow vesicles. The diameter of the trachea in adults is from one-half to three-fourths of an inch when at rest. THE LARYNX The larynx may be regarded as the funnel-shaped termination of the trachea. It enlarges upward and is composed of various cartilages more or less mobile, connected by ligaments and moved by muscles. The exterior of the larynx is formed by the I. Thyroid cartilage. II. Cricoid cartilage. The cartilages in the interior are: I. The Arytenoid cartilages. II. Cartilages of Wrisberg. III. Cartilages of Santorini. IV. Cuneiform cartilages. To the cartilages of the larynx must be further added the Epiglottis, with the little cartilage at the centre of its inner side.