352 RUDIMENTARY SOUNDS. 



an alternate pressure and relaxation 

 upon the tracheal tubes. The air, 

 thus passing in and out, throws into 

 vibration the valves of the spiracle, 

 which, as seen in Fig. 180, are sus- 

 pended upon a dozen or more flexible 

 supports ; but their free edges, ap- 

 proaching within a certain distance of 

 each other, are thrown into quick vi- 

 bration by the passing current, in the 

 same manner as is the vibrating spring 

 of the accordeon. These vibrating 

 plates of insects are the rudiments of 



Spiracle of insect what ^ become fa perfect ^ ap _ 



paratus in man. Again, in others, the swiftly-recurring beating of the 

 wings produces a sound, as, for example, in the musquito. Among ver- 

 tebrated animals, those which breathe the air are vocal, nearly all fishes 

 Sounds of rep- being mute. From fishes, as we pass upward, the sound 

 tiles and birds. an( j t ne instrument which makes it increase together in com- 

 plexity. Through a simple chink, the air expelled from the respiratory 

 sacs of snakes, by the contraction of their abdominal muscles, issues 

 forth as a mere hiss, the sound being increased in the frog by the devel- 

 opment of resonant cavities. From these simple noises we are conduct- 

 .ed to the musical notes of birds, some of which are of exquisite purity 

 and sweetness. In these, the vocal glottis is situated at the bifurcation 

 of the trachea, another glottis being above for the final es- 

 cape of the air. These vertebrated animals first introduce 

 us to the mechanism for articulate speech, the rav&n and parrot being 

 able to pronounce words with distinctness. The articulation is effected, 

 as in man, by the motions of the tongue and other portions of the mouth. 

 For the further consideration of this subject, it is necessary to under- 

 Distinction be- s ^ an( ^ tnat there i g a distinction between song and speech, 

 tween song and Song is produced by the glottis, speech by the mouth; or, 

 speech. perhaps, a more correct statement would be, that the larynx 



is the organ of song, the mouth of that form of speech which we call 

 whispering, and for which nothing is required but a stream of air issuing 

 from the fauces, the tongue and other organs giving it articulation ; but 

 for audible speech, a noise is created in the larynx, and modified by ar- 

 ticulation in the mouth. 



The double larynx of birds is replaced by a single larynx in man, 

 which serves at the same time for the entrance and exit of air, and like- 

 wise for vocalization. Those birds in which the lower larynx is absent 

 are voiceless. A general idea of the construction of the organ of voice 



