cricoid cartilage, on each side, is a small piece of
triangular shape, called the _arytenoid cartilage_. Each arytenoid is
movable on the cricoid and is connected with one end of a vocal cord.

[Fig. 150]

Fig. 150--*Vocal cords* as seen from above. _A._ In producing sound, _B._
During quiet breathing.

*The Vocal Cords* are formed by two narrow strips of tissue which,
connecting with the thyroid cartilage in front and the arytenoid
cartilages behind, lie in folds of the mucous membrane. They have the
general appearance of ridge-like projections from the sides of the larynx,
but at their edges they are sharp and smooth. The open space between the
cords is called the _glottis_. When sound is not being produced, the
glottis is open and has a triangular form, due to the spreading apart of
the arytenoid cartilages and the attached cords. But when sound is being
produced, the glottis is almost completely closed by the cords. Above the
vocal cords, and resembling them in appearance, are two other folds of
membrane, called the _false vocal cords_ (B, Fig. 149). The false cords do
not produce sound, but they aid in the closing of the glottis.

*How the Voice is Produced.*--The voice is produced through the vibrations
of the vocal cords. A special set of muscles draws the arytenoid
cartilages toward each other, thereby bringing their edges very near and
parallel to each other in the passage. At the same time other muscles act
on the thyroid and cricoid cartilages to separate them at the top and give
the cords the necessary tension. With the glottis now almost closed,
blasts of air from the lungs strike the sharp edges of the cords and set
them in vibration (Fig. 150). The vocal cords do not vibrate as strings,
like the strings of a violin, but somewhat as reeds, similar to the reeds
of a French harp or reed organ.

The location of the vocal cords in the air passages enables the lungs and
the muscles of respiration to aid in the production of the voice. It is
their function to supply the necessary force for setting the cords in
vibration. The upper air passages (mouth, nostrils, and pharynx) supply
resonance chambers for reenforcing the vibrations from the vocal cords,
thereby greatly increasing their intensity. In ordinary breathing the
vocal cords are in a relaxed condition against the sides of the larynx and
are not acted upon by the air as it enters or leaves t