LARYNX AND PEG NATION. 353 



closure ; we shall discover, however, that the contraction of 

 this muscle has to fulfil another and very important func- 

 tion. 



We have not mentioned an extrinsic or exterior muscle of 

 the larynx, called the crico-thyroid. The influence exerted 

 by it over the glottis is unimportant : it causes the thyroid 

 cartilage to rock forwards, rotating it forwards and down- 

 wards on the cricoid cartilage; this action, although it elon- 

 gates the glottis by elongating the fibrous parts leading from 

 the inner surface of the thyroid to the anterior apophysis of 

 the arytenoid cartilages, has not this effect in phonation, aa 

 direct experiment has proved. The functions of this muscle 

 appear to be connected rather with deglutition than with 

 phonation, the muscle itself being innervated by the same 

 nerve as the constrictor muscle of the pharynx (superior la- 

 ryngeal nerve, external branch). 



Mechanism of Phonation. Experiments upon animals, 

 accidental observation in the case of man, and attempts at 

 artificial phonation made with detached larynges, all prove 

 that the sound of the voice is produced in the glottis. In 

 forming this sound, we know that the glottis contracts : thus, 

 it was at first supposed that the vocal organ, in its inner 

 mechanism, resembled a whistle, the sound being produced 

 by the vibration of the air in passing through a small orifice, 

 and becoming sharper in proportion to the smallness of the 

 orifice. 



It is now proved that it is not the air, but the edges of 

 the glottis, w T hich vibrate in this organ ; the larynx, therefore, 

 rather resembles a reed-pipe than a whistle. There is, 

 however, another analogous organ, which also acts like a 

 reed ; this is the buccal orifice, the lips, which vibrate as in 

 playing the horn, for instance ; it is needless to show the 

 anatomical analogy between the orifice of the mouth and that 

 of the glottis. 1 



In order to vibrate, however, the edges of the glottis must 

 be tense. It was supposed that the vocal cords adjoining the 

 mucous were stretched by the contraction of certain muscles. 

 Miiller made the experiment of causing a rapid current of air 



1 " There is no authority for comparing the inferior thyro- 

 arytenoid fold either to cords or ribbons: it is much better to call 

 them simply inferior folds, or, if an anatomical name be desired, 

 more expressive of their configuration and function, the vocal lips." 

 L. M'andl, " Traite Pratique de3 Maladies du Larynx et du 

 Tiarynx." Paris, 1872.) 



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