LARYNX, the collection of structures by which the voice is partially produced, situated at the upper part of the trachea or windpipe. It is formed mainly by two pieces of cartilage, the thyroid above and the cricoid, which is situated below. The thyroid is formed of two Extended wings like plates meeting at the Middle line in front and making a prominence known as Adam's apple; above and from the sides two horns project upward, and are con nected by bands to the hyoid bone, from which the larynx is suspended. The thyroid cartilage rests and is movable upon the cricoid, moving backward or forward, but not from side to side. The cricoid cartilage is shaped like a signet-ring (Greek krikos, a ring), the narrow part of the ring being in front. The cricoid carries, perched on its upper edge behind, the arytenoid i cartilages, which are of great im portance n the production of the voice. These various cartilages form a framework upon which muscles and mucous membranes are posed. The mucous membrane which lines the larynx is thrown into various folds. These folds about 15 mm. long in man and 11 mm. in woman are called the true vocal cords, and by their movements the voice is produced. Pro jecting toward the middle they form a chink, which is called the glottis. By the contraction
of various muscles this chink can be so brought together that the air forced through it throw the edges of the membrane into vibration and so produce sounds. Variations in the form of the chink will effect changes in the sound. Thus the production of voice is the same as in musical instruments, the arrangement of the many complicated muscles in the larynx being such as to produce (1) the vibratory sounds, •(2) to regulate the sound, (3) to vary the pitch, and (4) to determine the quality of the sound. While the voice is produced in the larynx, it is modified by the rest of the respira tory passages. (See Voice). In the act of swallowing, the glottis is covered by a cartilag inous plate called the epiglottis. In the accom panying cut, • Fig. 1, shows c, the larynx inter nally, being the epiglottis situated above the glottis or entrance to the larynx, A A the trachea, and D the oesophagus or gullet. In Fig. 2, y is the trachea, a the hyoid bone, N N the thyreo-hyoid membrane, o the thyreo-hyoid ligament, G the thyroid cartilage, a the cricoid cartilage, P the crico-thyroid ligament. See NOSE AND THROAT.