PHYSIOLOGY OF THE VOCAL ORGANS.
597. In the formation of the voice, each part already described performs an important office. The cricoid and thyroid cartilages give form and stability to the larynx; the arytenoid cartilages, by their movement, vary the width of the glottis. The epiglottis is flexible and elastic. When it is erect, the chink of the glottis is open, as in inspiration; when depressed, as in swallowing food and drink, it covers and closes this aperture. It prevents the introduction of articles of food into the trachea, and probably modifies sound as it issues from the glottis.
598. The muscles of the neck elevate and depress the larynx; the muscles of the larynx increase or diminish the width of the glottis; at the same time, the vocal cords are 273 relaxed or tightened, while the muscles of the face open and close the mouth.
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?
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.
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.