320 STUDIES IN PHYSIOLOGY 



is not the case, however, for the music of birds is produced 

 in a special organ, the syr'inx (Greek, meaning a pipe), 

 which is found where the lower end of the windpipe divides 

 to form the bronchi (Fig. 146). Here the air tubes enlarge, 

 and the cartilage rings extend little more than half around 

 the windpipe and the bronchi. Tense membranes complete 

 the wall of the air tubes, on their inner side, and act as 

 resonators. Within these tubes are several transverse mem- 

 branes which are vibrated much like the vocal cords of man. 

 The trilling note of certain birds is probably produced by 

 the movements of a semilunar membrane stretched around 

 the sides of the lower part of the windpipe. 



The croaking of frogs is produced by vibration of vocal 

 cords at the sides of the glottis opening, and the volume of the 

 sound is largely increased by the resonating cavities formed 

 by the lungs and the croaking sacs. The latter open near 

 the angle of the jaws on either side. Most reptiles and 

 fishes produce no vocal sounds whatever. 



Among the group of insects one finds many different 

 methods of producing noises. None of these, however, can 

 be called vocal, for they are not produced by organs which 

 resemble at all a larynx. Flies, mosquitoes, and many other 

 insects produce a sound by the rapid movements of their 

 wings ; grasshoppers scrape the rough edges of their wings 

 together; while the cicada has a very complex organ on each 

 side of its body by which it produces its deafening clatter. 



