464 MUSCULAR MOTION. 



These muscles, too, are only the proper muscles of the larynx, or those 

 restricted in their attachments to its five cartilages. They are but a 

 few of the muscles of voice. In speaking, we use a great many more. 

 Fifteen pairs of different muscles, attached to the cartilages or os 

 hyoides, and acting as agents, antagonists, or directors, are constantly 

 employed in keeping the cartilages steady, regulating their situation, 

 and moving them as occasion requires, upwards and downwards, back- 

 wards and forwards, and in every intermediate direction, according to 

 the course of the fibres, or in the diagonal between different fibres. 

 These muscles, 'independently of the former, are susceptible, it is cal- 

 culated, of upwards of 1,073,841,800 different combinations; and, when 

 they co-operate with the seven pairs of the larynx, of 17592186,044,415 ; 

 exclusive of the changes that must arise from the different degrees of 

 force, velocity, &c., with which they may be brought into action. But 

 these muscles are not the whole that co-operate with the larynx in 

 the production of voice. The diaphragm, abdominal muscles, inter- 

 costals, and all, that directly or indirectly act on the air, or on the 

 parts to which the muscles of the glottis or os hyoides are attached, 

 contribute their share. The numerical estimate would, consequently, 

 require to be largely augmented. Mr. Bishop computes the number of 

 muscles brought into action at the same time in the ordinary modula- 

 tions of the voice to be one hundred. 1 Such calculations are, of 

 course, only approximate; but they show the inconceivable variety of 

 movement of which the vocal apparatus is directly or indirectly sus- 

 ceptible. 



The tone of the voice has been a great stumbling-block to the physi- 

 ologist and physicist. The mode, in which it is produced, and the 

 parts more immediately concerned in the function, have been the 

 object of various theories or hypotheses, regarding the voice. 



Galen, under his theory, that the larynx is a wind instrument of the 

 flute kind, of which the glottis is the beak and the trachea the body 

 of the flute, ascribed the variety of tones to two causes to variation 

 in the length of the musical instrument, and in the embouchure. In 

 the theory of Dodart, in which the human vocal instrument was likened 

 to a horn, the inferior ligaments of the glottis being compared to the 

 lips of the performer, no importance was attached to variation in the 

 length of the instrument. He attributed variety of tones to simple 

 alteration in the embouchure or mouth-piece, in other words, to 

 changes in the size of the glottis, by the action of its appropriate mus- 

 cles; and the rising and falling of the larynx, he regarded as serving 

 no other purpose than that of influencing mechanically the size of the 

 aperture of the glottis; whilst Ferrein, who regarded the larynx as a 

 stringed instrument, accounted for the variety of tones by different 

 degrees of tension and length of the inferior ligaments of the glottis or 

 vocal cords. In the production of acute tones, these cords were 

 stretched and shortened. For grave tones, they were relaxed, and 

 lengthened. He was of opinion, that the length of the vocal tube had 

 no influence on the tone. 



1 The London and Edinburgh Philosoph. Magazine, &c., for Sept., 1836, p. 209. 



