

LARYNX AND PHONATION. 355 



body, we shall certainly not fix upon the mucous, which 

 forms a protecting envelope, but is not an organ capable of 

 being stretched or of vibrating. The vocal cord, although 

 it is called a ligament, does not seem to exhibit the neces- 

 sary conditions for constituting the vibrating cord, as is gen- 

 erally supposed. This ligament is composed of elastic tissue, 

 that is, of fibres which are not rectilinear, but entangled in 

 every direction, so that, whichever way it is drawn, the ten- 

 sion produced is extremely slight. In the physiological state, 

 however, this tension, which is accompanied by the contrac- 

 tion of the glottis, can only be produced by the crico-thyroid 

 muscle, which, we have seen, plays a very insignificant part 

 in phonation. The muscular tissue then remains, viz., the 

 thyro-arytenoid muscle. Now the muscular tissue is very 

 susceptible of tension. What can be more stretched, or more 

 strongly elastic, or what more vibratory than a contracted 

 muscle ? The thyro-arytenoid muscle, therefore, in a physio- 

 logical point of view, constitutes the true vocal cord, the only 

 real vibratory element among the tissues which form the lips 

 of the glottis. This vocal cord is stretched, for the purpose 

 of vibration: this is not, however, the effect of any outside 

 influence : it contracts of itself. 1 The glottis apparently forms 

 a pipe which vibrates by contraction and not by tension. As 

 being the source of sound, this organ is unequalled (unique), 

 and cannot be imitated artificially, since we cannot make 

 muscle : the lips (orbicular muscle of the buccal orifice) work 

 in a similar manner in the cases previously mentioned. 2 



We shall easily understand the use of the vocal elastic 

 cord, if we consider what would happen if the organ of phona- 

 tion or voice were composed only of muscle, covered with a 

 mucous surface : at each contraction of the former, the latter 

 would form irregular folds, thus altering the sound of the 

 voice; this happens when the smallest particle of foreign 

 matter, whether mucus or any thing else, is caught in the 

 glottis. An elastic organ is therefore necessary to render the 

 muscle and the mucous independent of each other, by inter- 

 posing itself between the two. This is precisely the office of 



1 " The contraction of the internal thyro-arytenoid muscle 

 causes the lower folds (lips of the glottis), which" were soft and 

 loose during respiration, to be transformed; during the emission of 

 the voice, into an organ-pipe, whose rigidity is in proportion to its 

 tonality. This muscle may therefore be said to be the accommo- 

 dating muscle of the voice." (L. Mandl. 1872.) 



2 See note, p. 353. 



