alled the arytenoid, which
are of great importance in the production of the voice. These cartilages
are capped with little horn-like projections, and give attachment at their
anterior angles to the true vocal cords, and at their posterior
angles to the muscles which open and close the glottis, or upper
opening of the windpipe. When in their natural position the arytenoid
cartilages resemble somewhat the mouth of a pitcher, hence their name.

351. The Vocal Cords. The mucous membrane which lines the various
cartilages of the larynx is thrown into several folds. Thus, one fold, the
free edge of which is formed of a band of elastic fibers, passes
horizontally outwards from each side towards the middle line, at the level
of the base of the arytenoid cartilages. These folds are called the true
vocal cords, by the movements of which the voice is produced.

Above them are other folds of mucous membrane called the false vocal
cords, which take no part in the production of the voice. The
arrangement of the true vocal cords, projecting as they do towards the
middle line, reduces to a mere chink the space between the part of the
larynx above them and the part below them. This constriction of the larynx
is called the glottis.

[Illustration: Fig. 150.--View of the Cartilages and Ligaments of Larynx.
(Posterior view.)

A, epiglottis;
B, thyroid cartilage;
C, arytenoid cartilage;
D, ligament connecting lower cornu of the thyroid with the back of the
cricoid cartilage;
E, cricoid cartilage;
F, upper ring of the trachea.
]

352. The Mechanism of the Voice. The mechanism of the voice may be
more easily understood by a study of Fig. 150. We have here the larynx,
viewed from behind, with all the soft parts in connection with it. On
looking down, the folds forming the true vocal cords are seen enclosing a
V-shaped aperture (the glottis), the narrow part being in front.

The form of this aperture may be changed by the delicately coordinate
activities of the muscles of the larynx. For instance, the vocal cords may
be brought so closely together that the space becomes a mere slit. Air
forced through the slit will throw the edges of the folds into vibration
and a sound will be produced.

The Variations in the form of the opening will determine the variations in
the sound. Now, if the various muscles of the larynx be relaxed, the
opening of the glottis is wider. Thus the air enters and leaves the larynx
during breat