scles of the face open and close the mouth.

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595. What difference between the formation of the larynx of the female
and that of the male? 596. Does this difference exist in childhood? Is
its development progressive? 597-600. _Give the physiology of the
vocal organs._ 597. Which cartilages give stability and form to the
larynx? Which vary the width of the glottis? What is the function of
the epiglottis? 598. What effect have the muscles of the neck upon the
larynx? The use of the muscles of the larynx?

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599. The elasticity of the ribs and the contraction of the abdominal
muscles diminish the cavity of the chest, and the air, in consequence,
is pressed from the air-cells into the bronchial tubes and trachea. It
then rushes by the vocal cords, and causes a peculiar vibration, which
produces _sound_.

_Observations._ 1st. Experiments have satisfactorily shown that the
vocal cords are the principal agents in the formation of the voice.
The tongue, which many have supposed to be the most important organ in
speaking, is not essential to sound. In several instances it has been
removed, and the persons thus mutilated could speak with fluency.

2d. When the vocal cords are ulcerated, or inflamed, however slightly,
as in sore throat produced by a cold, the voice will be changed. The
loss of speech among public speakers is generally produced by a
relaxation of the vocal ligaments. Hence, bronchitis is a misnomer for
this affection.

600. Sound is varied by the velocity of the expelled current of air,
and the tension of the vocal ligaments. The size of the larynx, the
volume and health of the lungs, the condition of the fauces and nasal
passages, the elevation and depression of the chin, the development
and freedom of action of the muscles which are attached to the larynx,
the opening of the mouth, the state of the mind, and general health of
the system, influence the modulations of sound.

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What effect has the combined action of these muscles? 599. How is
sound produced? What have experiments shown? What effect has disease
of the vocal ligaments upon the voice? 600. How is sound varied?
Mention other conditions that contribute to the modulation of sound.

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CHAPTER XXX.

HYGIENE OF THE VOCAL ORGANS.

601. _The voice can be changed and modified by habit._ Sailors,
smiths, and others, who are engaged i