| 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 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.
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.
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.