ACTIONS OF THE LARYNX. 



461 



of vibrating strings, or of flute pipes. There would seem, at first sight, to be 

 a marked difference in character, between the Chordae Vocales, and the tongue 

 of any reed instrument ; but this difference is really by no means considera- 

 ble. In a reed, elasticity is a property of the tongue itself, when fixed at one 

 end, the other vibrating freely ; but by a membranous lamina, fixed in the 

 same manner, no tone would be produced. If such a lamina, however, be 

 made elastic by a moderate degree of tension, and be fixed in such a manner 

 as to be advantageously acted on by a current of air, it will give a distinct 

 tone. It is observed by Miiller, that membranous tongues made elastic by 

 tension, may have either of three different forms, i. That of a band extended 

 by a cord, and included between two firm plates, so that there is a cleft for 

 the passage of air on each side of the tongue, u. The elastic membrane 

 may be stretched over the half or any portion of the end of a short tube, the 

 other part being occupied by a solid plate, between which and the elastic 

 membrane a narrow fissure is left. HI. Two elastic membranes may be ex- 

 tended across the mouth of a short tube, each covering a portion of the opening, 

 and having a chink left open between them. This last is evidently the form 

 most allied to the Human Glottis ; but it may be made to approximate still more 

 closely, by prolonging the membranes in a direction parallel to that of the cur- 

 rent of air, so that not merely their edges, but their whole planes, shall be 

 thrown into vibration. Upon this principle, a kind of artificial Glottis has 

 been constructed by Mr. Willis ; the conditions of action, and the effects ot 

 which, are so nearly allied to that of the real instrument, that the similar cha- 

 racter of the two can scarcely be doubted. The following is his description 

 of it. "Let a wooden pipe be prepared of the form of Fig. 198 a, having a 

 foot, c, like that of an organ-pipe, and an upper opening, long and narrow, as 

 at B, with a point A, rising at one 



end of it. If a piece of leather, or Fig. 198. 



still better, of sheet India-rubber, be a b 



doubled round this point, and secur- 

 ed by being bound round the pipe 

 at D with strong thread, as in Fig. 

 198, b, it will give us an artificial 

 glottis, with its upper edges G H, 

 which may be made to vibrate or 

 not, at pleasure, by inclining the 

 planes of the edges. A couple of 

 pieces of cork, E, F, may be glued 

 to the corners, to make them more 

 manageable. From this machine, 

 various notes may be obtained, by 

 stretching the edges in the direction 

 of their length, G H ; the notes rising 

 in pitch with the increased tension, 

 although the length of the vibrating 

 edge is increased. It is true, that a 

 scale of notes equal in extent to that 

 of the human voice, cannot be ob- 

 tained from edges of leather ; but 



this scale is much greater in India-rubber than in leather ; and the elasticity 

 of them both is so much inferior to that of the vocal ligaments, that we may 

 readily infer that the great scale of the latter is due to its greater elastic pow- 

 ers." By other experimenters, the tissue forming the middle coat of the arte- 

 ries has been used for this purpose, in the moist state, with great success ; 

 with this, the tissue of the vocal ligaments is nearly identical. It is worthy 



39* 



Artificial Glottis. 



