The Mechanism of the Human Voice Part 3

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

SIDE VIEW OF THE VOICEBOX, OR LARYNX.

1, 2. RING-SHIELD MUSCLE (CRICO-THYROIDEUS).

3. LID.

4. SHIELD.

5, 6. UPPER HORNS OF THE SHIELD.

7. RING.

8. WINDPIPE.

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

SIDE VIEW OF THE VOICEBOX, OR LARYNX, SHOWING THE INTERIOR OF THE LEFT HALF.

1, 2, 3. SHIELD-PYRAMID MUSCLE (THYRO-ARYTENOIDEUS).

4, 5. RING-PYRAMID MUSCLE (CRICO-ARYTENOIDEUS).

6. SHIELD.

7. LEFT UPPER HORN.

8. PYRAMID.

9. RING.

10. WINDPIPE.

It may be observed here that it is impossible to imitate, in the dead subject, the contraction of the vocal muscles. All conclusions, therefore, drawn from experiments upon exsected larynges, with regard to tone-production in living man are necessarily quite untrustworthy, and cannot for one moment be admitted as evidence against observations made upon singers with the laryngoscope.

These two pairs of muscles, then, namely the ring-shield muscles (pl.

VIII, 1, 2) and the shield-pyramid muscles (pl. IX, 1, 2, 3) by stretching, slackening, and compressing the vocal ligaments, mainly govern the pitch of the tones produced by their vibrations. The ring-shield muscles receive some a.s.sistance in stretching the vocal ligaments from another quarter, of which we shall speak later on.

We have now had a look at the vocal ligaments, and we have seen by what means they are put on the stretch. As, however, in a state of repose these ligaments diverge behind, they must be brought parallel to each other before they are ready for the production of sound. Let us, therefore, in order to explain how this is done, imagine that we have cut off that part of the pyramids which is standing out above the vocal ligaments (pl. VII), and let us now have a look at these parts from above. You see the ligaments (pl. XA, 1, 2), a section of the pyramids (pl. XA, 3, 4), and uniting these an elastic band (pl. XA, 5). The s.p.a.ce between these parts is commonly called the Glottis, but as this appellation belongs more properly to the vocal ligaments, it is manifestly wrong to give the same name to the _s.p.a.ce_ which they inclose. This s.p.a.ce should be distinguished as the "_c.h.i.n.k_ of the Glottis" or the "Vocal c.h.i.n.k."

I have been blamed for making this distinction in the face of almost universal usage. But I can point to the great anatomist Professor Luschka as having set the example, and while it is true that in most physiological works "Glottis" is used for the _slit_ between the vocal ligaments, yet the appellations "Rima glottidis"

and "Aperture of the glottis" are also employed for the same thing.

Medical men, moreover, speak of "Spasm of the glottis," and singing masters of the "Shock of the glottis," which terms are clearly quite meaningless when applied to a s.p.a.ce.

Dr. Garrett says, on page 12 of the book quoted before, that "The upper portion of the larynx above the false vocal cords is termed the glottis." He might as well say, "The upper portion of the face above the nose is termed the mouth." I really should not notice so astounding a statement were it not made by one signing himself an M.D., and published by so eminent a firm of Medical publishers as Messrs. J. and A.

Churchill.

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

A. GLOTTIS IN REPOSE.

B. GLOTTIS IN RESPIRATION.

C. GLOTTIS IN THE PRODUCTION OF SOUND.

A. 1, 2. VOCAL LIGAMENTS.

3, 4. SECTION OF THE PYRAMIDS.

5. ELASTIC BAND.

6, 7. LEVERS OF THE PYRAMIDS.

On plate XI you see all parts in a state of rest. To the levers of the pyramids (pl. XI, 1, 2) a pair of muscles is attached, the bases of which are fixed upon the back of the ring cartilage below (pl. XI, 3, 6, 3). The action of these "Back Ring-Pyramid Muscles" (pl. XI, 4, 1 and 5, 2) is to contract as soon as we take breath, thereby drawing together the pyramids _behind_ and separating them _in front_, at the same time stretching the elastic band behind (pl. X, A, 5). By this movement the c.h.i.n.k of the glottis is thrown _wide open_ into the shape depicted on pl. X, B. During expiration these relax, the elastic band contracts, and the vocal c.h.i.n.k resumes the shape as on pl. XI. These movements go on from the beginning of our lives to the end, whether we are asleep or awake, with more or less vigour, according as we take a slight or a deep inspiration. The back ring-pyramid muscles (pl. XI, 4, 1 and 5, 2), have consequently the all-important function of keeping open the gate through which the air we breathe enters the lungs. They have, therefore, been poetically called the "Guardians of the Portal of Life." By their action of pulling the pyramids backwards, they also a.s.sist the ring-shield muscles (pl. VIII, 1, 2) in stretching the vocal ligaments.

In opposition to these "Opening Muscles" there is another pair rising from the side borders of the ring (pl. XI, 3, 3) which are fastened to the front part of the levers of the pyramids (pl. XI, 1, 2), serving to draw together their front projections to which the vocal ligaments are attached, and which are thereby brought parallel with each other.

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

VIEW OF A SECTION OF THE VOICEBOX, OR LARYNX, FROM ABOVE.

1, 2. SECTION OF THE PYRAMIDS WITH VOCAL LIGAMENTS AND ELASTIC BAND.

3, 6, 3. RING.

7. PYRAMID MUSCLE (ARYTENOIDEUS TRANSVERSUS).

8, 9, 10. SHIELD.

11. BANDS BY MEANS OF WHICH THE PYRAMIDS ARE ATTACHED TO THE RING.

4 & 5. BACK RING-PYRAMID MUSCLES (POSTERIOR CRICO-ARYTENOIDEI).

1, 3 & 2, 3. SIDE RING-PYRAMID MUSCLES (LATERAL CRICO-ARYTENOIDEI).

NOTE.--The shield-pyramid muscles (Thyro-Arytenoidei) which run parallel with the vocal ligaments are, for the sake of clearness, omitted from this diagram.]

These "Side Ring-Pyramid Muscles" (pl. XI, 3, 1 and 3, 2; see also pl.

IX, 5, 4) are a.s.sisted by a single muscle uniting the pyramids behind the elastic band which we have already noticed. This muscle we will call the "Pyramid Muscle" (pl. XI, 7). By the united action of the muscles which have just been described the vocal c.h.i.n.k is thrown in the shape shown on pl. X, C, and the vocal ligaments are now in a proper position for the production of tone.

Before proceeding any farther it will be well if we once more glance at the muscles with which we have become acquainted, so that we may be quite sure about their functions.