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aperture of the glottis will be V-shaped, the point of the V being forwards, and the base behind.
For, in front, or in the angle of the thyroid, the two vocal ligaments are fastened permanently close together, whereas, behind, their extremities will be separated as far as the arytenoids, to which they are attached, are separated 1
I. View of the human larynx from above as actually seen by the aid of the
instrument called the laryngoscope : A, in the condition when voice is
being produced ; B, at rest, when no voice is produced. e. Epiglottis (foreshortened). c.v. The vocal chords. c.v s. The so-called false vocal chords, folds of mucous membrane lying
above the real vocal chords. a. Elevation caused by the arytenoid cartilages. s.w. Elevations caused by small cartilages connected with the arytenoids. 1. Root of the tongue. II. Diagram of the same. from each other. Under these circumstances a current of air passing through the glottis produces no sound, the parallelism of the vocal chords being wanting ; whence it is that, ordinarily, expiration and inspiration take place quietly. Passing from one arytenoid cartilage to the other, at their posterior surfaces are certain muscles called the posterior arytenoid (Fig. 58, Ar.p.). There are also two sets of muscles connecting each arytenoid with the cricoid, and called from their positions respectively the posterior and lateral crico-arytenoid (Fig. 58, C.a.p., Ca.l.). By the more or less separate or combined action of these muscles, the arytenoid cartilages and, consequently, the hinder ends of the vocal chords attached to them, may be made to approach or recede from each other, and thus the vocal chords rendered parallel or the reverse.
We have seen that the crico-thyroid muscle pulls the thyroid cartilage down, and thus increases the distance between the front of the thyroid and the back of the cricoid, on which the arytenoids are seated. This movement, the arytenoids being fixed, must tend to pull out the vocal chords lengthways, or in other words to tighten them.
Running from the re-entering angle in the front part of the thyroid, backward, to the arytenoids, alongside the vocal chords (and indeed imbedded in the transverse folds, of which the chords are the free edges) are two strong muscles, one on each side (Fig. 58, Th.A.), called thyroarytenoid. The effect of the contraction of these muscles is to pull up the thyroid cartilage after it has been depressed by the crico-thyroid muscles, and consequently to slacken the vocal chords.
Thus the parallelism (6) of the vocal chords is determined chiefly by the relative distance from each other of the arytenoid cartilages; the tension (c) of the vocal cords is determined chiefly by the upward or downward movement of the thyroid cartilage ; and both these conditions are dependent on the action of certain muscles.
The current of air (d) whose passage sets the chords vibrating is supplied by the movements of expiration, which, when the chords are sufficiently parallel and tense, produce that musical note which constitutes the voice, but otherwise give rise to no audible sound at all.
25. Other things being alike, the musical note will be lo v or high, according as the vocal chords are relaxed or tightened ; and this again depends upon the relative predominance of the contraction of the crico-thyroid and thyro-arytenoid muscles. For when the thyro-arytenoid muscles are fully contracted, the thyroid cartilage will be pulled up as far as it can go, and the vocal chords will be rendered relatively lax ; while, when the crico-thyroid muscles are fully contracted, the thyroid cartilage will be depressed as much as possible, and the vocal chords will be made more tense.
The range of any voice depends upon the difference of tension which can be given to the vocal chords, in these two positions of the thyroid cartilage. Accuracy of singing depends upon the precision with which the singer can voluntarily adjust the contractions of the thyroarytenoid and crico-thyroid muscles—so as to give his
Fig. 6o. Diagram of a model illustrating the action of the levers and muscles of the larynx. The stand and vertical pillar represent the cricoid and arytenoid cartilages, while the rod (bc), moving on a pivot at c, takes the place of the thyroid cartilage; a b is an elastic band representing the vocal ligament. Parallel with this runs a cord fastened at one end to the rod b c, and, at the other, passing over a pulley to the weight B. This represents the thyroarytenoid muscle. A cord attached to the middle of b c, and passing over a second pulley to the weight A, represents the crico-thyroid muscle. It is obvious that when the bar (6 c) is pulled down to the position c d, the elastic band (a b) is put on the stretch.
vocal chords the exact tension at which their vibration will yield the notes required.
The quality of a voice—treble, bass, tenor, &c.-on the other hand, depends upon the make of the particular larynx, the primitive length of its vocal chords, their elasticity, the amount of resonance of the surrounding parts, and so on.
Thus, men have deeper notes than boys and women, because their larynxes are larger and their vocal chords
longer-..whence, though equally elastic, they vibrate less swiftly.
26. Speech is voice modulated by the throat, tongue, and lips. Thus, voice may exist without speech; and it is commonly said that speech may exist without voice, as in whispering. This is only true, however, if the title of voice be restricted to the sound produced by the vibration of the vocal chords ; for, in whispering, there is a sort of voice produced by the vibration of the muscular walls of the lips which thus replace the vocal chords. A whisper is, in fact, a very low whistle.
The modulation of the voice into speech is effected by changing the form of the cavity of the mouth and nose. by the action of the muscles which move the walls of those parts.
Thus, if the pure vowel sounds-
O (as in or); O (as in oh), 00 (as in cool), are pronounced successively, it will be found that they may be all formed out of the sound produced by a continuous expiration, the mouth being kept open, but the form of its aperture, and the extent to which the lips are thrust out or drawn in so as to lengthen or shorten the distance of the orifice from the larynx, being changed for each vowel. It will be narrowest, with the lips most drawn back, in E, widest in A', and roundest, with the lips most protruded, in 00.
Certain consonants also may be pronounced without interrupting the current of expired air, by modification of the form of the throat and mouth.
Thus the aspirate, H, is the result of a little extra expiratory force--a sort of incipient cough. S and 2, S! and ) (as in jugular G soft, as in gentry), Th, L, Ř, F, V, may likewise all be produced by continuous currents of air forced through the mouth, the shape of the cavity of which is peculiarly modified by the tongue and lips.
27. All the vocal sounds hitherto noted so far resemble one another, that their production does not involve the stoppage of the current of air which traverses either of the modulating passages.
But the sounds of M and N can only be formed by blocking the current of air which passes through the mouth, while free passage is left through the nose. For M, the mouth is shut by the lips ; for N, by the application of the tongue to the palate.
28. The other consonantal sounds of the English language are produced by shutting the passage through both nose and mouth ; and, as it were, forcing the expiratory vocal current through the obstacle furnished by the latter, the character of which obstacle gives each consonant its peculiarity. Thus, in producing the consonants B and P, the mouth is shut by the lips, which are then forced open in this explosive manner. In T and D, the mouth passage is suddenly barred by the application of the point of the tongue to the teeth, or to the front part of the palate; while in K and G (hard, as in go) the middle and back of the tongue are similarly forced against the back part of the palate.
29. An artificial larynx may be constructed by properly adjusting elastic bands, which take the place of the vocal chords ; and, when a current of air is forced through these, due regulation of the tension of the bands will give rise to all the notes of the human voice. As each vowel and consonantal sound is produced by the modification of the length and form of the cavities, which lie over the natural larynx, so, by placing over the artificial larynx chambers to which any requisite shape can be given, the various letters may be sounded. It is by attending to these facts and principles that various speaking machines have been constructed.
30. Although the tongue is credited with the responsibility of speech, as the "unruly member," and undoubtedly takes a very important share in its production, it is not absolutely indispensable. Hence, the apparently fabulous stories of people who have been enabled to speak, after their tongues had been cut out by the cruelty of a tyrant, or persecutor, may be quite true.
Some years ago I had the opportunity of examining a person, whom I will call Mr. R., whose tongue had been removed as completely as a skilful surgeon could perform the operation. When the mouth was widely opened, the truncated face of the stump of the tongue, apparently