erfect harmony.

There are certain articulate sounds called vowel or vocal, from the fact
that they are produced by the vocal cords, and are but slightly modified
as they pass out of the mouth. The true vowels, _a, e, i, o, u_, can
all be sounded alone, and may be prolonged in expiration. These are the
sounds chiefly used in singing. The differences in their characters are
produced by changes in the position of the tongue, mouth, and lips.

Consonants are sounds produced by interruptions of the outgoing
current of air, but in some cases have no sound in themselves, and serve
merely to modify vowel sounds. Thus, when the interruption to the outgoing
current takes place by movements of the lips, we have the _labial_
consonants, _p_, _b_, _f_, and _v_. When the tongue, in relation with the
teeth or hard palate, obstructs the air, the _dental_ consonants, _d_,
_t_, _l_, and _s_ are produced. _Gutturals_, such as _k_, _g_, _ch_, _gh_,
and _r_, are due to the movements of the root of the tongue in connection
with the soft palate or pharynx.

To secure an easy and proper production of articulate sounds, the mouth,
teeth, lips, tongue, and palate should be in perfect order. The
modifications in articulation occasioned by a defect in the palate, or in
the uvula, by the loss of teeth, from disease, and from congenital
defects, are sufficiently familiar. We have seen that speech consists
essentially in a modification of the vocal sounds by the accessory organs,
or by parts above the larynx, the latter being the essential vocal
instrument.

Many animals have the power of making articulated sounds; a few have
risen, like man, to the dignity of sentences, but these are only by
imitation of the human voice. Both vowels and consonants can be
distinguished in the notes of birds, the vocal powers of which are
generally higher than those of mammals. The latter, as a rule, produce
only vowels, though some are also able to form consonants.

Persons idiotic from birth are incapable of producing any other vocal
sounds than inarticulate cries, although supplied with all the internal
means of articulation. Persons deaf and dumb are in the same situation,
though from a different cause; the one being incapable of imitating, and
the other being deprived of hearing the sounds to be imitated.

[Illustration: Fig. 153.--Direction of Pull of the Lateral
Crico-Arytenoids, which adduct the Vocal Cords. (Dotted lines show
position in adduction.)]