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    ORGANS OF THE THORACIC CAVITY

    311. What are the organs, and their construction, in the thoracic cavity?HBH 144.4

    The heart is one of these organs, but this we have already noticed in connection with the circulatory system, and shall have occasion to speak of it again after examining the action of the lungs. In the functions of respiration or breathing, and speaking, the organs used are the trachea or wind-pipe, lungs and diaphragm.HBH 144.5

    312. What is the organ of voice?HBH 144.6

    The structure composed of muscle and cartilage, at the upper part of the wind-pipe, called the larynx, is the apparatus of voice; while the lungs and trachea are the organs of respiration.HBH 144.7

    313. What is the larynx, and where is it situated?HBH 145.1

    There is a funnel-shaped cavity back of the roots of the tongue, at the upper part of the wind-pipe, called the pharynx. This cavity is open from above, with canals coming from the nose, and the eustachian tubes from the ears; just in front of these is the pendulous body called the palate; in anatomy it is called the vail of the palate. In the act of swallowing, it is pressed back, closing the nasal canals and the eustachian tubes, so that nothing can pass into them. A little lower down, near the roots of the tongue, in the front part of the pharynx, opens the larynx, or the mouth of the wind-pipe. This is so situated that everything which is swallowed must pass directly over it. To prevent any of the food or drink from entering the wind-pipe, a small, oval-shaped valve of cartilage, called the epiglottis, is placed over it. This valve is always raised, except in the act of swallowing, when it shuts down over the orifice, and completely closes it for an instant, while the food or other substances are passing over it; then it immediately opens, that breathing may not be interfered with. It is in the larynx that all the modifications of the voice are produced, by the air passing through it from the lungs.HBH 145.2

    314. What is the construction of the larynx?HBH 145.3

    It is a short tube, of an hour-glass form, composed of cartilages, ligaments, muscles, vessels, nerves, and mucous membrane. The larynx is composed of five cartilage; the first of these produces, at the upper part of the neck, the prominence called Adam’s apple. The larynx has twelve ligaments, or vocal cords, attached in front to the receding angle of the thyroid cartilage, and extending backward. It has eight muscles; these are used in opening and closing the glottis, and in regulating the position and tension of the vocal cords. The mucous membrane of the larynx is the same as that of the mouth, which is prolonged through it into the bronchial tubes and the lungs. The arteries are the superior and inferior thyroid. The nerves are branches of the pneumogastric.HBH 145.4

    315. How are the different tones of the human voice produced?HBH 146.1

    The voice is formed in the larynx, and all its modifications are produced by the simple expulsion of air from the lungs, when the vocal ligaments or cords are held in a certain degree of tension. The sound is occasioned by the vibration of the vocal ligaments. Speech is a modification of voice-sounds in the cavity of the mouth. The articulating organs are the tongue, palate, lips and teeth. The cavities of the nose also modify the speech. The English language may be reduced to forty-four rudimental sounds, or elements, sixteen of which are vowels, and twenty-eight are consonants. The muscles which stretch or relax the vocal ligaments are alone concerned in the voice. The pitch of the tones is regulated by the tension of the vocal cords. The volume or intensity depends on the capacity of the lungs, length of the trachea, or wind-pipe, and the force with which the air is expelled, and the flexibility of the vocal cords. In the male the vocal cords are longer than in the female, in the proportion of three to two, which renders the male voice usually an octave lower. The natural compass of voice, in most persons, is two octaves, or twenty-four semitones. Singers are capable of producing ten distinct intervals between each semitone, making 240 intervals, requiring as many different states of tension of the vocal cords, all of which are producible at pleasure, and without a greater variation of the length of the cords than one-fifth of an inch. One of the most wonderful feats accomplished in the human body, is the precision with which the will determines the exact degree of tension necessary to produce a given note in an instant of time, after the mind has decided the note required. How sad to think that an instrument so nicely and wonderfully constructed as the human voice, should ever be used in defaming its Maker, or harshly speaking to our fellow creatures.HBH 146.2

    316. What is necessary in training the human voice?HBH 147.1

    If speech is defective, the precise cause must be noticed, and the difficulty be removed, or overcome by exercise. If persons stammer, induce them to speak with the mouth open, and with the lungs filled with air. If they lisp, reading and speaking with the teeth closed will help it. Reading aloud, shouting, singing, and laughing, are healthful exercises, promoting digestion, and giving action to the lungs and abdominal muscles.HBH 147.2

    THE TRACHEA, OR WIND-PIPE.HBH 147.3

    317. What is the trachea?HBH 147.4

    It is the wind-pipe, which extends from the larynx down to the third dorsal vertebra, where it divides into the right and left branch. The right passes off to the upper part of the right lung at nearly right angles; the left is smaller, and descends obliquely beneath the arch of the aorta, to the left lung. It is kept in a distended form by twenty-four cartilaginous rings, connected with each other by a membranous texture. These rings are not entire circles, but about one-third of the circle, and that on the back side, directly in front of the oesophagus or meat pipe, is occupied by a membranous texture of muscular fibers running in the direction of the rings, so that their contraction decreases the caliber of the wind-pipe. When the food is descending the meat-pipe this muscular portion yields, so that the passage of the food is not obstructed, as would be the case if the rings passed entirely around. As the branches of the wind-pipe become subdivided in the substance of the lungs, these rings become softened down, and gradually disappear, leaving nothing but the membranous forms of the air tubes.HBH 147.5

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