228 HABITS OF BIRDS. 



hand, the chords or reeds are indeed rectangular, 

 but they are fixed by three sides instead of one. In 

 the common reeded instrument, again, we raise or 

 lower the notes by varying its length ; while, in the 

 plates of the vocal reeds, it is the size which is 

 varied. In musical instruments, besides, we cannot 

 employ nor procure reeds, the plates of which can 

 every instant alter their thickness and elasticity as 

 happens in the vocal chords. It can easily be con- 

 ceived, then, from these circumstances, that the vocal 

 chords may produce and vary the tones of the voice 

 somewhat after the manner of reeded instruments, 

 though we cannot make out the analogy in every 

 particular. 



M. Majendie partly proved these views by actual 

 observation ; and, in the instance of dogs, he found 

 that, when the sound uttered was grave, the vocal 

 chords vibrated through their whole length, arid the 

 expired air passed through the whole extent of the 

 orifice (glottis). When the sounds were acute, on 

 the other hand, the vocal chords did not vibrate in 

 the front, but only in the back part ; and, as the 

 orifice was of course diminished, the air only passed 

 through the vibrating portion. When the sounds, 

 again, became very acute, the vocal chords no longer 

 vibrated, except at the very extremity, and the ex- 

 pired air then passed out only at this part. So far 

 as he was able to ascertain, the sound increased in 

 acuteness till the orifice became entirely closed. When 

 the air could no longer pass, the sound ceased. 



That it is the vocal chords whose vibration pro- 

 duces the sound, may also be fairly inferred from 

 experiments made after death ; for by taking the 

 windpipe of any quadruped and blowing strongly 

 from below upwards, no sound will be produced so 

 long as the orifice remains expanded : but if, while 

 continuing to blow, the orifice is compressed so much 



