The vocal instrument may be said to consist of three parts: (1) the bellows; (2) the membranous reed contained in the larynx, which by the actions of groups of muscles can be altered in tension and thus variation in pitch determined; (3) the resonator, which consists of the mouth, the throat, the larynx, the nose, and air sinuses contained in the bones of the skull, also the windpipe, the bronchial tubes, and the lungs. The main and important part of the resonator, however, is situated above the glottis (the opening between the vocal cords, _vide_ fig. 6), and it is capable of only slight variations in length and of many and important variations in form. In the production of musical sounds its chief influence is upon the quality of the overtones and therefore upon the timbre of the voice; moreover, the movable structures of the resonator, the lower jaw, the lips, the tongue, the soft palate, can, by changing the form of the resonator, not only impress upon the sound waves particular overtones as they issue from the mouth, but simultaneously can effect the combination of vowels and consonants with the formation of syllables, the combination of syllables with the formation of words, and the combination of words with the formation of articulate language. The reed portion of the instrument acting alone can only express emotional feeling; the resonator, the effector of articulate speech, is the instrument of intelligence, will, and feeling. It must not, however, be thought that the vocal instrument consists of two separately usable parts, for phonation (except in the whispered voice) always accompanies articulation.