OF THE HUMAN VOICE. 
559 
out the analogy between the laws of stretched cords and those of the vocal liga- 
ments, it is not intended that those ligaments should be considered as stringed 
instruments, but only that this analogy is accurate so far as relates to the velocity 
with which an impulse is propagated along them. Dodart supposed the tension of 
the vocal cords to be merely subservient to an alteration in the size of the aperture of 
the glottis, and that the difference of yjth of a fibre of silk, or 3-g^th of a hair in the 
dimensions of that aperture, was sufficient to alter the pitch of the voice ; but this has 
been so completely refuted by more recent physiologists, and is so directly at variance 
with acoustic principles, that we need not give illustrations of its fallacy. M. Savart 
considered that the action of the air in its passage through the ventricles of the 
larynx, between the superior and inferior ligaments, is really the source of sound, 
and analogous to the mechanism of the bird-call or dog-whistle*. There is certainly 
a great resemblance in the structure of that instrument to the space above-mentioned 
in many of the higher animals, which might easily have led to this ingenious hypo- 
thesis ; but, as we find neither superior ligaments nor ventricles of Morgagni in many 
of the order Ruminantia, in which the voice is very sonorous, this theory (as Muller 
remarks) is untenable. 
We next come to the consideration of the alleged analogy between the action of 
the vocal ligaments and that of the reeds of musical instruments. This opinion is 
maintained by MM. Biot, Cagniard la Tour, Majendie, Malgaigne, Muller and 
several other distinguished scientific men. It is opposed principally by M. Savart, 
who observes that the essential principle of the action of reeds consists in the periodi- 
cal opening and shutting of the orifice through which the stream of air passes, but 
tnat this is wanting in the glottis ; and that were the latter a reed, the edges of the 
thyro-arytenoid ligaments which form the sides of the chink would be alternately 
forced asunder by the column of air in the larynx, and brought together by their 
tension; whereas, he found by experiment, that air blown through the glottis pro- 
duced sound although its edges were from one-sixth to one-fourth of an inch asunder. 
M. Savart has however clearly mistaken the circumstance wherein the essential prin- 
ciple of reeds consists, since those of the clarionet, bassoon, hautbois, &c. do not en- 
tirely close the apertures through which the breath passes ; and this is likewise the case 
with the natural reed formed by the lips of players on the flute and horn. There is 
in all probability a double action of the vocal cords in the production of sound ; the 
one being a vibratory motion throughout their length similar to that of a musical 
string, and the other an oscillation like that of a reed, forming a partial opening and 
closing of the glottis. The author is led to adopt this view of the functions of the vocal 
organs from considering that every circumstance which he has established in his 
previous investigation of their action when treated as cords, is perfectly consistent 
with the hypothesis of their vibrating like the tongues of reeds ; for let us now sup- 
pose them to be simply membranous tongues. In this case the axis of motion is the 
* See Plate XXX. fig. 1', g. 
