The Mechanism of the Human Voice Part 4

MUSCLES:

I. GOVERNING THE SHAPE OF THE VOCAL c.h.i.n.k.

The Back Ring-Pyramid} OPENING Muscles } THE VOCAL c.h.i.n.k.

THESE ARE OPPOSED BY--

The Side Ring-Pyramid } Muscles, and the Pyramid} CLOSING Muscles, a.s.sisted by the} THE VOCAL c.h.i.n.k.

s.h.i.+eld-Pyramid Muscles }

II. GOVERNING THE PITCH OF THE TONES.

The Ring-s.h.i.+eld Muscles, } STRETCHING a.s.sisted by the Back Ring-Pyramid } Muscles } THE VOCAL LIGAMENTS.

THESE ARE OPPOSED BY--

The s.h.i.+eld-Pyramid } SLACKENING Muscles } THE VOCAL LIGAMENTS.

=The Pocket Ligaments= (called "False Vocal Cords," pl. XII, 1 and 2) are a pair of horizontal projections running above and parallel with the vocal ligaments (pl. XII, 3 and 4). The pocket ligaments are, like the vocal ligaments, attached in front to the s.h.i.+eld and behind to the pyramids. They may be described as two ledge-shaped pads mainly formed of glands. They are very sensitive and movable, and ready on the smallest incitement to meet with great rapidity in order to protect the vocal ligaments from any harm. They must, therefore, be chiefly regarded as safeguards of the vocal apparatus, though it is probable that by breaking the stream of air pa.s.sing through the c.h.i.n.k of the glottis, they also exercise considerable influence upon the _quality_ of the tone emitted. It may be affirmed, however, without the slightest hesitation, that they have absolutely nothing to do with the _production_ of tone.

We shall see these glandular ledges again during our observations upon the living subject, and I shall therefore say no more about them at present.

[Ill.u.s.tration: PLATE XII.

VIEW OF THE VOICEBOX, OR LARYNX, WHICH HAS BEEN CUT OPEN FROM BEHIND.

1, 2. POCKET LIGAMENTS (FALSE VOCAL CORDS).

3, 4. VOCAL LIGAMENTS (VOCAL CORDS).

5, 6. s.h.i.+ELD (THYROID) CARTILAGE.

7, 8. CARTILAGES OF SANTORINI.

9. LID (EPIGLOTTIS).

14, 10 & 15, 11. FOLDS OF MUCOUS MEMBRANE (ARYTENO-EPIGLOTTIC FOLDS).

12, 13. WEDGES (CUNEIFORM CARTILAGES).

14, 15. CARTILAGES OF WRISBERG.

16, 17. PYRAMID MUSCLE (ARYTENOIDEUS TRANSVERSUS).

18, 19. RING (CRICOID) CARTILAGE.

20, 21. TONGUE (HYOID) BONE.

The s.p.a.ce between the pocket ligaments and the vocal ligaments (pl. XII, 1, 2, 3, 4) is the entrance to two pouches or pockets which extend outwards and upwards. The dimensions of these pockets vary very much in different individuals. As a rule their height does not exceed two-fifths of an inch, so that their terminations do not reach the upper borders of the s.h.i.+eld cartilage (pl. XII, 5 and 6). But there are instances in which the pockets are nearly three-quarters of an inch high, and where such is the case they, as a necessary consequence, reach beyond the s.h.i.+eld. Sometimes they are so high as nearly to touch the root of the tongue. Their outer walls are chiefly formed of loose fatty cellular tissue, and the pockets are almost entirely surrounded by a large number of small glands.

Now these are the "Laryngeal sacculi" which, according to Mr.

Illingworth, produce the falsetto voice by "acting in the same way as a hazel-nut can be made to act as a whistle, when the kernel has been extracted through a small hole in the sh.e.l.l," &c. I think, however, that the reader will, from the description given above, agree with me that the acoustic properties of the pockets of the voicebox cannot be very great, and that, at all events, there is a vast difference between their construction and that of a hazel-nut, either with or without the kernel. Then there is this additional difficulty, that even if one could whistle upon the pockets in the manner suggested, there are two of them, covered, let it be remembered, with a mult.i.tude of glands, continually producing moisture, and liable to enlarge or to diminish. How, I should like to know, could two such cavities be so tuned as under any circ.u.mstances to produce exactly the same tones? Would not rather frightful discords be the inevitable result? And again, what provision is there in the pockets for the gradations of pitch? But quite apart from these considerations, this and other similar theories are completely disproved by the fact that every tone which the human voice is capable of producing can be produced by _inspiration as well as by expiration_. The tones sung by inspiration are, as might be expected, wholly devoid of beauty, because the vocal apparatus is, as it were, put upside down, and the position of bellows and resonator reversed. But that does not alter the question. The fact remains, and clearly proves that the pockets have no more to do with the falsetto than with the chest voice, because in inspiration the air strikes the vocal ligaments _after it has pa.s.sed_ the pockets, and yet the result is, beauty of tone apart, exactly the same.

The function of the pockets, in my opinion, is this: They are the means of isolating the vocal ligaments, thus enabling them to vibrate freely and without hindrance. They also allow the sound-waves to expand sideways, thereby materially adding to their resonance. Lastly, they with their many little glands produce and supply the vocal ligaments with that moisture without which, according to the investigations of J.

Muller,[H] the production of tone cannot be carried on.

Above the pocket ligaments there is a kind of tube which is formed by the upper part of the pyramids (surmounted by two little bodies called the cartilages of Santorini, pl. XII, 7, 8) behind; the lid or epiglottis (pl. XII, 9) in front, and sideways by two folds of mucous membrane running up from the pyramids to the lid (pl. XII, 14, 10 and 15, 11). These folds are in many cases supported by two small cartilages, which we will call the Wedges (pl. XII, 12, 13). These, according to Madame Emma Seiler, are the chief factors in the formation of the highest register of the female voice. In some physiological works they are treated as of very little consequence, and in others they are not mentioned at all.

These wedges are two thin strips of cartilage running in front of the pyramids (pl. XII, 12 and 13) where they are embedded in a number of glands. Their upper ends terminate in the cartilages of Wrisberg (pl.

XII, 14, 15), and their lower ends gradually dwindle away in the direction of the vocal ligaments.

Madame Seiler says that they "reach to the middle of the vocal chords, by which they are enveloped."[I] She comments in the same book on the fact that German anatomists have been reluctant to admit the existence of these cartilages; and she adds on page 61, "It was, therefore, a great satisfaction to me to find them described under the name of the cuneiform cartilages in Wilson's 'Human Anatomy.'" It must be confessed, however, that Wilson's description of them is totally different from Madame Seiler's. He says, "The cuneiform cartilages are two small cylinders of yellow fibro-cartilage, about seven lines in length and enlarged at each extremity. _By the lower end or base_ the cartilage is attached _to the middle of the external surface_ of the arytenoid (the pyramid), and by its upper extremity forms a prominence in the border of the aryteno-epiglottidean fold of membrane"[J] (_i.e._, the fold running up to the lid). According to Seiler, therefore, the wedges reach from the pyramids to the middle of the vocal ligaments, but according to Wilson their bases are attached to the middle of the outer surface of the pyramids, so that they cannot even touch the vocal ligaments. As Madame Seiler a.s.signs very important functions to these wedges in the formation of the highest register of the female voice, and as she quotes Wilson in a manner that must lead the reader to suppose he gave a similar description to hers of these cartilages, I have thought it right to give Wilson's statement in full.

But there is a description of these cartilages by Dr. Witkowski which corresponds very closely with Madame Seiler's. Speaking of some of the glands of the voicebox, he says in the work mentioned before, on p. 12--"They are arranged in the form of an L, whose vertical branch goes along the arytenoid cartilages (the pyramids), _the horizontal branch following the direction of the vocal cords_.

_There is often found situated in the midst of this group of glands the cuneiform cartilage of Wrisberg_, sometimes reduced to a mere cartilaginous granule."

Dr. Elsberg also describes them on p. 37 of the treatise before mentioned as "elongated nodules" in the hinder portion of the vocal ligaments, and says they are found "more often in the female than in the male s.e.x." He calls them the "posterior vocal nodules," and gives on p. 36 a diagram which shows them most clearly and unmistakably. This point would therefore seem to be settled.

=The Resonator.=--We now come to the last part of our instrument, namely, the resonator, which is formed of (1) the pockets of the larynx; (2) the tube above the pocket ligaments; (3) the upper part of the throat; (4) the mouth; and (5) the nose. Before giving a description of the resonator, it will be necessary to make a few introductory remarks on certain laws of the philosophy of sound, which have been so clearly demonstrated that they admit of no contradiction.

=Tone=, as we have seen, is the result of rapid periodic vibrations.

The =Loudness= of tone depends upon the _amplitude_ of the vibrations.

This is easily shown by drawing a bow over the string of a violin: while the vibrations of the string are largest, the tone produced is loudest, and as the vibrations get smaller, so the tone becomes fainter.

The =Pitch= of tone depends upon the _number_ of vibrations in a given period of time. The greater the number of vibrations the higher the pitch, and _vice versa_.

The =Quality= of tone depends on the _form_ of the vibrations, "which also determines the occurrence of upper partial tones."[K]

Now, to make the sound of any tone-producing element more intense, and to give it some special quality, is the work of the resonator. If we simply fix a fiddle string at either end, and, after giving it a certain amount of tension, draw a bow across it, we shall certainly produce a tone, but a very poor and faint one. Put the same string with the same amount of tension upon a cheap violin, and the tone will be intensified, and its quality changed, though that quality may be of a very unpleasant kind. Repeat the experiment upon an Amati or a Straduarius, and not only will the tone be more powerful still, but it will also have a full, round, and beautiful quality. Something, it is true, depends upon the string and upon the bowing, but we are here supposing the same string and the same player, our object being to show how the _resonator_, which, in this case, is the body of the violin, intensifies the tone of the string, and affects its quality.

Ill.u.s.trations exemplifying the same thing might be multiplied to any extent, but the one I have just given will suffice. As with the string, so with the vocal ligaments. Cut a larynx out of a dead body, put it in proper position on the top of a bellows, and force the air through it, and you will produce tone, but faint and poor tone. Now add a resonator to the larynx, and the tone of the vocal ligaments will be intensified, and its quality altered according to the kind of resonator you make use of.

It is clear, therefore, that the human voice does not only depend upon the vibrations of the vocal ligaments, and the corresponding vibrations of the air pa.s.sing between them, but also upon the resonator as defined on p. 9. According to the natural formation of our resonator, and according to the infinite variety of shapes which every one has it in his power to give to it, our voices will be, always supposing the conditions of the vocal ligaments to be the same, either full, round, sonorous, and _beautiful_, or they will be poor, cutting, m.u.f.fled, guttural, nasal, and _ugly_.

As we have, or may easily acquire, absolute command over the resonator, or, at least, over the greatest part of it, it is a comfort to know that so very much depends upon it, and I trust my readers will now, with some amount of pleasure, look with me at this part of the vocal apparatus.

The 1st and 2nd divisions of the resonator--namely, the pockets of the larynx and the tube above the pocket ligaments--have been fully described on pp. 52, 53, and no more need be said on the subject here.

The upper part of the throat, called in scientific works the "Pharynx"

(pl. I, P), is a cavity, the largest part of which may be seen through the arch at the back of the open mouth. Its hinder wall is formed by the spinal column, and it extends upwards as far as the Eustachian tubes (pl. I, E) which communicate with the middle part of the ear. Here it joins--

The =Cavities of the Nose= (pl. I, N), which have for their base the hard and soft palate (pl. I, H and S), and which are divided by a bone part.i.tion.

The only part of the =Mouth= which requires a particular description is the soft palate. This is a movable part.i.tion by means of which either the mouth or the nose can be completely separated from the throat. If the nose is to be shut off from the throat the soft palate is _raised_, and pressed against the back of the pharynx. If the mouth is to be shut off the soft palate is _lowered_, and rests closely upon the back of the tongue. This part.i.tion plays a most important part in vocalization. In the formation of all pure vowel sounds it is _raised_, thereby closing the nasal cavities, and it has been found that the closure is loosest for "ah" (as in "father") and tightest for "e" (as in "bee"), the intermediate vowels being "a" (as in "name"), "oh" and "oo" (as in "food"). This has been clearly shown by Czermak in the following manner.

Lying down on his back, he had the nasal cavities filled with tepid water. He then uttered the various vowel sounds, and ascertained from the quant.i.ty of water required to force open the closure formed by the soft palate the degree of tightness for each vowel. He afterwards constructed a very ingenious little apparatus, by means of which, in one of his lectures, he demonstrated this fact to his audience. It will be easily understood from the above explanation that, if the closure of the nasal cavities is sufficiently imperfect to allow any considerable amount of air to pa.s.s through the nose, the result will be a nasal tone.