VOICE. 



1501 



without experiments conclude the latter to be 

 the organ of sound. 



The superior larynx nevertheless performs 

 an important office, both preventing the passage 

 of the food into the wind-pipe* and modifying 

 the sound of the voice. It can be opened 

 and closed with rapidity, in singing birds ; 

 and is actively employed in the production of 

 melody : we can easily witness its simultaneous 

 movements with the mouth, in the song of 

 the canary, linnets, and others. Its influence 

 on the pitch is according to Savart, but little, 

 not amounting to more than a semitone. The 

 inferior larynx may be considered a reed 

 prefixed to a tube. The salient laminae of 

 the membrana tympaniformis, and the mem- 

 brana semilunaris are especially adapted to 

 produce a series of vibrations, when a current 

 of air is forced into the bronchi. It is indeed 

 only necessary to dissect out the vocal tube of 

 a bird, (such as that of the goose for example), 

 and blow into it by the mouth, to elicit 

 sounds. In the singing birds, which have the 

 lower larynx furnished with the most elaborate 

 muscular apparatus, the tension of the vibra- 

 tile membrane of the glottis can be regulated 

 with precision, so as to enable them to effect the 

 varied melodies which nature or art dictates. 

 In order to prove the duplex structure of the 

 inferior larynx, Savart divided the recurrent 

 nerve on one side in the living bird, after 

 which it continued to sing with all the modi- 

 fications of its melody as before. We agree as 

 to the duplex office of the lower larynx in 

 singing birds ; but in them the semilunar 

 membrane appears common to both sides, as 

 is also the os transversale. Savart considered 

 the semilunar membrane to be chiefly de- 

 veloped in those birds which have the most 

 reedy quality of voice, the speaking birds for 

 instance, such as the jays, pies, &c., but that, 

 in the production of the flute tones in singing 

 birds, it is more relaxed, and the glottis more 

 open. He observes that, in making a trans- 

 verse section of the trachea in the living bird, 

 which also cuts the recurrent nerve, and pro- 

 duces a relaxed state of the glottis, the 

 sounds become less ' criard,' and less ' sourd* ; 

 but, as birds thus maltreated suffer greatly, he 

 recommends the section of the recurrent nerve 

 only. It is one of the most difficult subjects 

 in acoustics to determine theoretically the 

 sound which many of the male Natatores ought 

 to produce, such, for example, as the Anas 

 domesticus, A. clangula, Mcrgus serrator, and 

 M. merganser, the structure of whose la- 

 rynges has been briefly described; and, when 

 we consider that these larynges are composed 

 of chambers of varied dimensions, bounded by 

 walls partly membranous and partly osseous, 

 the membranes being of unequal area, and 

 perhaps unequal tension, we may have some 

 notion of the extreme difficulty of the inquiry, 

 when some of the greatest mathematicians of 

 the past and present age have as yet been un- 

 able to determine analytically the law of the 

 vibration of a single piece of stretched parch- 

 ment, like the drum. 



Experiment shows that a single membranous 



stretched disc will produce many other, be- 

 sides its fundamental and harmonic sounds ; 

 we need not, therefore, be surprised at the 

 discordant tones which many of the Natatores 

 are well known to produce. The reason why 

 short tubes, such as the tracheas of many 

 small birds, produce tones of a very grave 

 pitch, has already been satisfactorily explained 

 by Savart. We observe, however, that, in those 

 birds in which the trachea is shortest, the 

 diameter smallest, and the walls very elastic, 

 the voice is most acute. The muscles 

 which vary the tension of the walls of the 

 vocal pipe are in continual action during the 

 modulation of the voice, in order to adjust the 

 tube of the trachea to the pitch of the glottis ; 

 but the number of vibrations is doubtless 

 determined by the glottis, and reinforced by 

 the walls of the pipe, as in Mammalia. The 

 cavities in the trachea of some of the Natatores 

 musi certainly influence the timbre, or qua- 

 lity of the voice of those birds. In the com- 

 mon crane, and other birds which have a con- 

 voluted trachea, the tones ought to be grave 

 in proportion to its length, if the number of 

 vibrations is determined by the length, as in 

 musical instruments. 



The voice of birds, as of other animals, is 

 always in a minor key ; but to describe the 

 melody of each bird would be foreign to our 

 subject. The range of notes is generally within 

 an octave, though they can greatly exceed it. 

 In the parrots, which have a voice of great 

 power, the inferior larynx is single. The two 

 membranes of the larynx leave a narrow chink 

 between them, through which the air is forced 

 from the lungs. These membranes, vibrating 

 in all their dimensions, produce that harsh and 

 disagreeable quality of sound peculiar to them. 

 They can also whistle, during which the glottis 

 is probably silent, and the column of air 

 vibrates as in a flute, when a vibratory move- 

 ment being communicated by the air, traverses 

 the elastic walls of the tube. Besides the 

 power of speech possessed by some birds, 

 many can imitate almost every sound they 

 hear. The blackbird has been known to imi- 

 tate the song of the nightingale, the crowing of 

 the common cock, and the cackle of the hen ; 

 the jay is said to mock the notes of the green- 

 finch and the neighing of the horse so closely, 

 that it was scarcely believed to be a bird by 

 those who heard it; also the calling of fowls to 

 their food, and the barking of the house dog. 

 The sounds uttered by birds are so various 

 that to describe them physiologically in detail 

 would occupy a volume ; let it therefore suf- 

 fice, in concluding this section of our article, 

 to mention that the voice of birds has been 

 made the theme not only of the naturalist, but 

 also of numerous eminent writers both in 

 prose and verse. 



VOICE OF REPTILES. The mechanism of 

 the vocal organs in reptiles presents very diver- 

 sified forms. The larynx varies considerably 

 in structure, not only in different orders, but 

 in different genera of the same family. It 

 would therefore be impossible to compress 

 within the limits assigned to this article the 



