1086 



THE VOICE. 



[BOOK in. 



in ascending scale successively shorter. The vocal cord, how- 

 ever, is not of such a permanent nature ; it undergoes under 

 the influence of muscular contraction changes other than those 

 of tension affecting its whole length ; its form may be altered 

 and the positions or attitudes which it may assume cannot be 

 described as simply those of greater or less distance from its 

 fellow along its whole length. It is in section as we have said 

 wedge-shaped ; and the projecting angle of the wedge may be 

 an open broad one, or a narrow acute one ; the vibrating cord 

 may be thick or thin ; and its vibrations will vary accordingly. 



The change from thick to thin is apparently brought about 

 by muscular contraction ; it has been suggested that a partial 

 contraction of some of the fibres of the thyro-arytenoid muscle, 

 external and also internal, more particularly of the bundles 

 which take a more or less vertical direction, produce the result ; 

 but the exact mechanism is by no means clear, though special 

 examination of the larynx shews that such a change of thick- 

 ness may take place. 



Again, there are reasons for thinking that contraction of the 

 internal thyro-arytenoid muscle as a whole affects the form and 

 the physical condition of the vocal cord, of which it furnishes 

 so to speak the body ; the strand of elastic fibres which forms 

 the surface of the cord lies upon the muscle somewhat after the 

 fashion of a fascia, and when the muscle, which in a state of 

 rest is somewhat curved with the concavity towards the glottis, 

 thickens and shortens in its contraction, carrying with it the 

 overlying layer of elastic fibres, it brings the whole cord into a 

 different form and different physical condition ; and this must 

 affect the character of the vibrations. Again, it is maintained 

 that some of the fibres of the internal thyro-arytenoid running 

 forward from the processus vocalis and outer surface of the 

 arytenoid are inserted into the layer of elastic fibres at varying 

 distances from the thyroid. If some of these bundles were to 

 contract by themselves they might render the front part of the 

 cord tense and the hind part relatively lax, or might modify in 

 particular parts that general tension of the whole cord which 

 was being effected by the crico-thyroid. 



Further, the closure of the glottis, the adduction of the 

 cords may take place in different ways, according as this or that 

 muscle or part of a muscle is being especially used. While the 

 vocal cords are being sufficiently approximated to allow the expira- 

 tory blast to throw them into vibrations the cartilaginous glottis 

 may remain fairly open, or may be nearly or quite closed ; 

 and each of these conditions must affect the voice in a different 

 way. Again, we have seen that the two vocal cords are close 

 together at their insertion into the thyroid, and diverge from the 

 middle line on each side so that the membranous glottis, when 

 the larynx is at rest, is an isosceles triangle. We might infer 



