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ceeding/rom the outside to the in, we reach a thick bundle of fibres, 

 perfectly horizontal, which line the outer aspect of the vocal liga- 

 ment, and which go from the anterior apophyses of the arytenoid 

 to the re-entering angle of the thyroid *. 



This bundle has its posterior half covered by the lateral crico- 

 arytenoid muscle, and its anterior half by the diverging fibres which 

 start from the thyroid. If we cut away the horizontal bundle in 

 successive layers, we see that the fibres are not all of the same 

 length ; the most external fibres are the longest, and the succeeding 

 ones get gradually shorter as they become more internal ; but they 

 all originate in the anterior cavity of the arytenoid, and the muscle 

 is inserted in the manner above explained throughout the whole 

 length of the vocal ligaments, the thyro-arytenoid portion of it ex- 

 cepted. As the fibres all begin from the arytenoid, and terminate 

 successively at more distant points of the membrane, we see that the 

 muscle is thicker behind than before. 



Thus the vocal ligament, and the membrane which depends from 

 it, the sole sources of all vocal sounds, are under the direct action of 

 the fibres which come from the anterior cavity of the arytenoid ; the 

 ligament under the action of the horizontal bundle, the membrane 

 under that of the oblique fibres. The long horizontal fibres, ex- 

 tending from one cartilage to the other, are placed at the exterior of 

 the short horizontal fibres, and at the interior of the oblique fibres. 

 The diverging fibres which start from the thyroid, acting only on 

 the superior vocal ligaments and the folds, seem to influence by 

 their contractions only the quality and volume of the voice. 



The remarkable arrangement of the fibres which we have just ex- 

 amined, enables us to explain a fundamental fact, the elevation of 

 the voice. The fibres of the horizontal bundle being placed over 

 each other, in layers, one covering the other, and getting gradually 

 longer and longer, as they become more external, extend their action 

 to the more anterior parts of the edges of the glottis. This progress- 

 ive action from the back to the front, encroaches gradually on the 

 length of the vibrating portion of the ligament, and likewise increases 

 its tension, and its faculty of accelerating its pulsations. 



Another portion of the thyro-arytenoid muscle at the same time 

 stretches and raises the vocal membrane more and more, causing a 

 * Another portion of the thyro-arytenoid muscle. 



