The mouth, that "channel of vocal utterance"

Mouth, from the Century Dictionary and Cyclopedia (1889-1991)

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[An excerpt from Vocal Sounds by Edward Search (1773):]

If on pronouncing u psilon you change to "au" you will find your under jaw drop, and your lips expand in a nearly circular form; if from thence to "o," you will find the corners of your lips draw in so as to turn into an oval; if to "u," you will find the orifice still more contracted, and the lips a little thrust forwards, the tongue in all these three operations lying close at the bottom of the mouth; if from thence you pass to "a," the lips at the corners will widen so as to form the long diameter of an ellipsis, the jaw remaining as before, and the tongue rising and spreading a very little; the transition thence to "e," is effected only by raising the hinder part of the tongue in the manner you did for an "h," and that to "i," by throwing the tongue into a convex, corresponding with the hollow roof of the mouth.