VOICE. 



H83 



the base of the cranium. By placing the 

 finder on the |)omum Adami this motion can 

 be easily felt, and at the same time the thyroid 

 cartilage is drawn up within the os-hyoides, 

 and presses on the epiglottis; the small space 

 between the thyroid and cricoid closes, the 

 pharynx is contracted, the velum palati is de- 

 pressed and curved forward, and the tonsils 

 approach each other : the reverse of these 

 phenomena takes place during the descent of 

 the voice. These are the principal pheno- 

 mena common to most mammalia which can 

 be recognised by external observation ; the 

 other changes being, on account of their situ- 

 ation, invisible. 



The effects of these variations on the tone 

 of the voice have been hitherto little under- 

 stood. It has always appeared incomprehen- 

 sible why the vocal tube should apparently 

 increase in length in the production of the 

 acute tones, and shorten in the grave ; a cir- 

 cumstance which theoretically presents an 

 acoustic paradox. Dodart and many ethers 

 have conceived the elevation of the larynx to 

 be merely for the purpose of shortening the 

 vocal tube in the supra- laryngeal cavity, and 

 have considered the trachea as producing no 

 effect on the pitch of the tone. Majendie 

 has also pointed out the shortening of this 

 part of the tube. In order to ascertain the 

 effect of these changes, the following expeii- 

 ments were made on the dead body. Having 

 laid bare the vocal organs of >n adult male, 

 I raised the larynx to the position it would 

 occupy by the elevation of the voice to an 

 octave, being about half an inch, and at the 

 same time minutely observed the position of 

 the lowest ring of the trachea with reference 

 to the sternum. By this operation 1 found the 

 trachea was raised out of the chest, nearly 

 to the same extent as the larynx had been 

 elevated towards the base of the skull. The 

 next step was to examine whether any change 

 had taken place in the diameter of the tube. 

 For this purpose, having measured the diame- 

 ter of the trachea in its natural position, the 

 larynx was again elevated to the same extent 

 as before, when the diameter was found 

 diminished one-third. These experiments 

 prove that, contrary to the general precon- 

 ception, the elevation of the larynx shortens 

 the tube independently of the contraction 

 between the thyroid cartilage and os-hyoides, 

 and at the same time lessens its diameter. 

 The same effects may easily be detected dur- 

 ing life by placing the finger on the trachea 

 immediately above the sternum during the 

 elevation of the larynx, when the trachea is 

 found to ascend out of the chest, and after- 

 wards to return to its former position ; a 

 movement in which the lungs and bronchi 

 participate. The alteration of the tube in 

 diameter may also be perceived by grasping 

 the trachea with the finger and thumb during 

 the elevation and depression of the larynx.* 

 These movements are so striking as to lead 



* Essays by the author, in the London and Edin- 

 burgh Philosophical Magazine, for September, Oc- 

 tober, and November, 1836. 



irresistibly to the conclusion, that there exists 

 a constant adaptation between the tension 

 and the vibrating length of the thyro-arytenoid 

 ligaments and the walls of the vocal tube, in 

 the production of tones of the ordinary re- 

 gister; for we have seen that the variations 

 of the vocal cords, at least as far as relates 

 to the modulation of sound, are perfectly in- 

 dependent of the length of the vocal tube, 

 and consequently the changes in its length 

 which we have just described are not at all 

 ncci-tsary for that purpose. Again, the vocal 

 tube is so short, that, as has been ascertained 

 by Weber and others, it could not, were it 

 rigid, affect the pitch of the note produced by 

 the glottis. As however this tube is com- 

 posed of flexible materials, its effects are 

 .similar to those observed in M. Savart's ex- 

 periments ; that is, the relaxed state of the 

 parietes compensates for its want of lengt' 1 , 

 and enables it to vibrate synchronously, and 

 therefore to give forth sounds equally grave 

 with those of the glottis, thereby reinforcing 

 the tone which would indeed be produced, 

 though with much less intensity, without this 

 aid. 



The Falsetto, or vocedi testa, has always been 

 considered a most embarrassing subject of re- 

 search, and its peculiar quality has excited the 

 attention both of the physiologist and of the 

 musician. Its most remarkable characteristic 

 consists in its being less reedy in tone, and 

 partaking nearly of the quality of the har- 

 monic sounds of stringed and wind instru- 

 ments. The change produced in the voice 

 when passing from the falsetto into the com- 

 mon tone, or the reverse, is in some persons 

 very sensible to the ear, whilst in others it is 

 almost imperceptible. Some individuals, more- 

 over, have the faculty of producing in the same 

 pitch as many as eight or ten tones, possessing 

 either the falsetto or the common character. 

 The falsetto has been generally ascribed to 

 some particular adaptation of the upper liga- 

 ments of the larynx. Dodart* has attempted 

 to prove that it is a supra-Iaryngeal function, 

 and that the nose becomes the principal tube 

 of sound instead of the cavity of the month. 

 Bennati -f also considered these tones as being 

 modulated by the supra-laryngeal cavity alone. 

 This hypothesis, however, is untenable, since 

 it supposes the column of air not to be in- 

 fluenced by the trachea, which is contrary to 

 experience. In order to detect some of the 

 movements of the larynx while the voice is 

 passing from the first to the second, or falsetto 

 register, it is only necessary to place the point 

 of the finger in the crico-tiiyroid chink, \\l,eii 

 it is found that at the moment the transition 

 from the primary to the secondary register 

 takes place, this chink, which was closed dur- 

 ing the production of the highest note of the 

 ordinary register, suddenly opens on the pro- 

 duction of the first note oi'the falsetto register, 

 and consequently the thyro-arytenoid liga- 

 ments are relaxed at the same moment the 



* Mem. de 1'Acad. 1707. 



f Rei-herches sur le Me'chanisme de la Yoix 

 humaine. 



