The part of the _larynx_ most concerned in producing the voice is the _glottis_, or narrow opening of the windpipe, having the _epiglottis_ suspended over it like a valve. The air expired from the lungs strikes upon the glottis, and thus becomes sonorous. The change that the glottis undergoes in the modulation of the voice has been matter of much controversy. Aristotle and Galen compared the glottis to a wind instrument; Ferrein assimilated it to a chorded one. This latter hypothesis was objected to, on the principle that a chord, to vibrate, should not only be in a state of tension, but dryness; characters which this organ does not possess, being constantly lubrified with mucus, and in a state of greater or lesser relaxation. Fulgentius considers the human voice to be composed of ten parts: the four first are the front teeth, so useful for the appulse of the tongue in forming sounds, without which a whistle would be produced instead of a voice; the fifth and sixth are the lips, which he compares to cymbals striking against each other; the seventh the tongue, which serves as a plectrum to articulate sounds; the eighth is the palate, the concavity of which forms the belly of the instrument; the ninth the throat, which performs the part of a flute; and the tenth the lungs, which supply the place of bellows. That every degree of action in the _glottis_ is due to the muscles of the _larynx_ is proved by the experiment of tying or dividing the recurrent nerves, when the voice is destroyed or weakened. Speech is a peculiar modification of the voice adjusted to the formation of the sounds of letters, by the expiration of the air through the nostrils and mouth, and in a great measure by the assistance of the tongue applied and struck against the neighbouring parts, the palate and front teeth in particular, and by the diversified action of the lips. This is Payne Knight's doctrine, in his analytical essay on the Greek alphabet, and an illustration of the notions of Fulgentius. Singing is compounded of speech and a musical modulation of the voice, a prerogative peculiar to man even in his most savage state; for, despite the assertions of the visionary Rousseau, who maintained that it is not natural to our species, we find that even in the uncivilized regions of Ethiopia, Greenland, and Kamtschatka, singing is a solace and a comfort. The mechanism of speech and articulation is so intricate, that even the division of letters and their distribution are attended with difficulties. The following is the division of Amman in his work _Surdus Loquens_, published at Amsterdam in 1629, and enlarged under the title of _Dissert. de Loquela_, 1700, and is, perhaps, the most natural and intelligible. He divides into, I. Vowels; II. Semi-vowels; III. Consonants. I. The vowels are _simple_, _a_, _e_, _i_, _o_, _u_; and _mixed_ _ae_, _oe_, _ue_: these are formed by the _voice_ only. The semi-vowels and consonants are articulated by the mechanism of _speech_.