26 



BRITISH BIRDS 



and the mammalia, but from a different part of that tube. In man 

 and in mammals the voice organ is placed in the throat just a 

 little way down, at the prominence often spoken of as ' Adam's 

 apple.' This is a wider part of the tube, with larger rings of cartil- 

 age, which contains a pair of tightly stretched membranes that can 

 be made to vibrate and cause a sound. In the bird, the voice organ 

 is situated farther down, at the very point where the trachea forks 

 mto the two bronchi, one for each lung. Here are figures which 

 illustrate the voice organ of a singing-bird (figs. 15, 16, 17). At 



Fio. 15.— Syrinx of Fio. 16.— Syrinx op Fm. 17.— Syrinx of 



Kaven (Posterior 

 Surface). 

 /, tynipaoiform membrane. 



Raven (Lateral 

 View). 



b, c, *, /, intrinsic 

 muscles ; d, sterno- 

 tracheal muscle. 



Raven cut open 

 longitudinally. 



<, pessulus ; h, vibrating 

 membrane; g, mem- 

 brana tympanif ormis. 



this forking of the trachea the rings of the tube, which are of 

 gristle or cartilage, become somewhat different in form. In the 

 middle is a piece, which is often converted into bone, like the 

 • three-way ' piece used to fix together the stick and the hoop of 

 cane of a butterfly-net. To the upper side of this, and therefore 

 within the tube, and directed upwards, is a little crescent-shaped 

 piece of membrane (A, fig. 17) ; this can be set vibrating by the 

 stream of air passing up and do^vn the windpipe. At the sides 

 of the syrinx there are shown in the figure (fig. 16) three pairs 



