COURTSHIP AMONG BIRDS 125 



production of peculiar and arresting sounds, musical and 

 otherwise. These are of two kinds : one wherein certain 

 feathers have been modified to produce rhythmical notes 

 either by percussion or by vibration ; the other wherein 

 the internal organs have been modified to produce musical 

 notes or loud, resonant cries. 



Instances of the latter kind are innumerable, and as a 

 consequence no more than one or two can be cited in 

 these pages. The facts associated with the production of 

 vocal, as distinct from instrumental, music are both 

 curious and puzzling. To begin with, this music is 

 produced by the lower end of the trachea or windpipe, 

 which has become modified in various ways, though not 

 so strictly in relation to the sounds produced as is 

 commonly supposed. The anatomical details of these 

 modifications cannot, or rather need not, be described 

 now, save in the most general terms. 



Briefly the syrinx, or organ of voice, of birds, is formed 

 in part by the lowermost rings which form the tubular 

 windpipe, and in part by the smaller pair of tubes which, 

 running therefrom to the lungs, form the bronchi. These 

 last are formed of semi-rings only, the inner wall of the 

 tube being formed by very delicate translucent membranes. 

 As air is forced from the lungs along the bronchi and up 

 the windpipe, the modulation of the voice is effected by 

 muscles which regulate the amount of air driven through 

 the syrinx, and the height of the column in the tube ; 

 the latter being effected by muscles which alternately 

 lengthen and shorten it. 



So far so good. Next it is to be noted that this syrinx 

 presents a great variety of modifications, or types, 

 differing not only in plan, but also in the number and 

 distribution of the muscles for its manipulation. The 



