tion of the air of these cavities, and so the pitch of the tone
produced. These chambers not having rigid walls, one can the better
understand that the tension of these parts may not only be different
in individuals, but vary in the same person from time to time,
according to the condition of his health, etc. Herein we find another
source of explanation of variations in the voice. All these
considerations make the resonance-chambers more important than ever,
so that there is greater objection to speaking of the larynx as _the_
vocal organ than we were aware of before these investigations were
undertaken.

SUMMARY.

Without a resonator, which may be solid or hollow, the sound made by a
reed or tense string is feeble. That the mouth can act as a resonator
may be proved by holding a vibrating tuning-fork of suitable pitch
before this chamber when open.

The resonating chambers of importance are supra-glottic. Of these the
"mouth" including all as far back as the pharynx and the nasal
chambers are the principal. These two main cavities are separated from
each other by the hard palate, which is a bony floor, covered with
mucous membrane, as are all the parts of the resonance-chambers. The
hard palate extends horizontally from the gums backward, and
is continued as the soft palate. The latter is a muscular and
therefore movable curtain that divides, with varying degrees of
completeness, the mouth (in the narrower sense) from the pharynx and
naso-pharynx--_i.e._, the space back of the soft palate and the
posterior nares (back nostrils) respectively. By the elevation of the
back of the tongue and the lowering of the soft palate as when one
speaks nasally, the mouth proper is largely shut off from the nasal
chambers, so that the breath must be directed through the nose. "Cleft
palate" also connects undesirably the mouth and nasal chambers. The
tonsils lie between two folds, the pillars of the fauces, connected
with the soft palate. When normal in size the tonsils should scarcely
extend beyond these folds. The uvula is the central lower tip of the
soft palate. The nasal chambers are divided by a central bony and
cartilaginous partition, the septum nasi, but are further encroached
upon, on each side, by three scroll-like (turbinated) bones. The
tongue is composed of several muscles, which explains why its
movements may be so complicated and delicate. The mouth cavity is
bounded in front by the gums, teeth, and lips.

The f