The Resonator.—­The resonator is an irregular-shaped tube with a bend in the middle; the vertical portion is formed by the larynx and pharynx, the horizontal by the mouth.  The length of the resonator, from the vocal cords to the lips, is about 6.5 to 7 inches (vide fig. 12).  The walls of the vertical portion are formed by the vertebral column and the muscles of the pharynx behind, the cartilages of the larynx and the muscles of the pharynx at the sides, and the thyroid cartilage, the epiglottis, and the root of the tongue in front; these structures form the walls of the throat and are all covered with a mucous membrane.  This portion of the resonator passage can be enlarged to a slight degree by traction upon the larynx below (sterno-thyroid muscle), by looseness of the pharyngeal muscles, and still more by the forward placement of the tongue; the converse is true as regards diminution in size.  The horizontal portion of the resonator tube (the mouth) has for its roof the soft palate and the hard palate, the tongue for its floor, and cheeks, lips, jaw, and teeth for its walls.  The interior dimensions of this portion of the resonator can be greatly modified by movements of the jaw, the soft palate, and the tongue, while the shape and form of its orifice is modified by the lips.

There are accessory resonator cavities, and the most important of these is the nose; its cavity is entirely enclosed in bone and cartilage, consequently it is immovable; this cavity may or may not be closed to the sonorous waves by the elevation of the soft palate.  When the mouth is closed, as in the production of the consonant m, e.g. in singing me, a nasal quality is imparted to the voice, and if a mirror be placed under the nostrils it will be seen by the vapour on it that the sound waves have issued from the nose; consequently the nasal portion of the resonator has imparted its characteristic quality to the sound.  The air sinuses in the upper jaws, frontal bones, and sphenoid bones act as accessory resonators; likewise the bronchi, windpipe, and lungs; but all these are of lesser importance compared with the principal resonating chamber of the mouth and throat.  If the mouth be closed and a tune be hummed the whole of the resonating chambers are in action, and the sound being emitted from the nose the nasal quality is especially marked.  But no sound waves are produced unless the air finds an exit; thus a tune cannot be hummed if both mouth and nostrils are closed.

From the description that I have given above, it will be observed that the mouth, controlled by the movements of the jaw, tongue, and lips, is best adapted for the purpose of articulate speech; and that the throat, which is less actively movable and contains the vocal cords, must have greater influence on the sound vibrations without participating in the articulation of words.  While the vocal cords serve the purpose of the reed, the resonator forms the body of the vocal instrument.  Every sound passes through it; every vowel and consonant in the production of syllables and words must be formed by it, and the whole character and individual qualities of the speaking as well as the singing voice depend in great part upon the manner in which it is used.