60 



All sounds are produced by a swift succession of 

 vibrations, from (he particles of sonorous bodies 

 which agitate the air. But the vibrations of the lips of 

 the glottis would not suffice to produce the neighing of 

 a horse. This begins by more or less acute interrupted 

 tones, accompanied by quaverings, and ends by tones 

 more or less grave, which is performed by jirks. This 

 second part is done by the lips of the glottis : the 

 other chiefly by a small, elastic membrane. This is 

 tendinous, very thin, of a triangular figure, and lies 

 flat on each extremity of th6 lips of the glottis. As it 

 adheres but loosely to these, it can easily flutter up 

 and down : and it is the play o/ the membrane up 

 and down, which produces the acute sounds of neigh-* 

 ing. These are more or less acute, as the membrane 

 is more or less thin, and its adhesion more or less 

 slack. The grave sounds that conclude the neighing, 

 are excited by the flutterings of the thick strings ; 

 which form the lips of the glottis. 



The hoarse sound of the ass's voice is not so much 

 produced by the lips of the glottis, as by a tendinous 

 part which adheres loosely on the aperture of a kind 

 of drum, situate under the extremity of the lips of the 

 glottis : above which are also found two large and 

 thick bags ; one on the right, the other on the left. 

 Each of these has a roundish aperture, cut much like 

 (he stopple of an organ. 



Such are the organs which form this amazing sound, 

 A kind of drum is the principal : and the two 

 bags above the lips of the glottis, are the main auxilia- 

 ries : while thos/e- lips, as plain experiment shew, con. 

 tribufevery little thereto. The mule's vaice much resem- 

 bles that of liis sire, and is formed by much the same 

 organs ; the drum of so singular a composition, being 

 found in mules also. 



There is another animal which affords us a particu- 

 lar disposition of the vocal organs. This is the hog : 

 whose shrill cries are more insupportable than his usual 

 grunting. Yet neither are these excited by the lips 

 of the glottis, bu* by the fluttering oi' t\vo large mem* 



