466 MUSCULAR MOTION. 



points. Like him, they do not consider the human larynx to consti- 

 tute a stringed instrument. They regard it as a variety of reed instru- 

 ment, but consider the vocal tube to be of moment in the production 

 of the voice. The objections they urge against the view of its resem- 

 bling a stringed instrument, are, the kind of articulation between the 

 arytenoid and cricoid cartilages, which admits of motion inwards and 

 outwards only; and they ask how the vocal cords can retain the length 

 requisite for the production of grave tones; and how they can elicit 

 sounds of a volume so considerable as those of the human voice? They 

 esteem it, consequently, a reed instrument of such nature as to be 

 capable of affording very grave tones with a pipe of little length ; and, 

 with slight variation of its length, susceptible, not only of furnishing a 

 certain series of sounds in harmonic progression, but all the imaginable 

 sounds and shades of sounds, in the compass of the musical scale which 

 each voice embraces. 



The theory of the reed instrument they apply to the vocal appara- 

 tus. The lips of the glottis are the reed, and the thyro-arytenoid mus- 

 cles render them fit for vibrating. In his experiments, made on living 

 dogs, M. Magendie saw, that when grave sounds were produced, the 

 ligaments of the glottis vibrated in their whole extent, and the expired 

 air issued through the whole of the glottis. In acute sounds, on the 

 other hand, they vibrated only at their posterior part, and the air 

 passed out through the part only that vibrated, the aperture being, 

 consequently, diminished ; and, when the sounds became very acute, 

 they vibrated only at their arytenoid extremity, and scarcely any air 

 issued ; so that tones beyond a certain degree of acuteness, cannot be 

 produced in consequence of the complete closure of the glottis. The 

 arytenoid muscle, whose chief use is to close the glottis at its posterior 

 extremity, he conceives to be the principal agent in the production of 

 acute sounds, and this idea was confirmed by the section of the two 

 laryngeal nerves that give motion to this muscle, which was followed 

 by loss of the power of producing almost all the acute tones; the 

 voice, at the same time, acquiring a degree of habitual graveness, which 

 it did not previously possess. The influence of contraction of the 

 thyro-arytenoid muscles on the tones is exerted in increasing or dimi- 

 nishing the elasticity of the ligaments, and thus, in modifying the 

 rapidity of the vibrations, so as to favor the production of acute or 

 grave tones. He thinks, too, that the contraction of these muscles 

 concurs greatly in closing, in part, the glottis, particularly its anterior 

 half; although the course of its fibres, it would appear, ought rather 

 to widen the aperture. The trachea or porte-vent has usually been 

 thought to exert no influence on the nature of the sound produced. It 

 has been conceived, however, by M. Grenie and others, that its elonga- 

 tion or decurtation may occasion some modification. 



Thus much for the part that resembles the reed MM. Biot and Ma- 

 gendie include in their theory of the voice the action of the vocal tube 

 likewise. This tube being, in man, capable of elongation and decurta- 

 tion, of dilatation and contraction, and of assuming an infinite number of 

 shapes, they think it well adapted, if placed in harmonic relation with 

 the larynx, for fulfilling the functions of the body of a reed instru- 



