Chapter 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 chink 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 chink 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 assist the ring-shield muscles (pl. VIII, 1, 2) in stretching the vocal ligaments.

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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.

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 assisted 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 chink 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.

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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.

MUSCLES: