VI 



FORM AND FUNCTION 



37 



important respects, the same as that of the human 

 larynx. There are two membranes corresponding to 

 those called in man the vocal chords, which can 

 be stretched tight, and made parallel to one another. 

 When thus stretched, they are set vibrating by the 

 passage of the air between them, and a note is pro- 

 duced. The syrinx is in principle a reed instrument, 



Mu 



Fig. 34.— Syrinx. 



Raven, a with bronchi ; a, b, c, half-rings ; where the two bronchi face each other 

 there is nothing but membrane, b, side view ; the outer part of the lower end of the 

 trachea and of the nearer bronchus being cut away; M, Membranous inner wall ot 

 bronchus; m.s, Membrana semilunaris; p, Pessulus ; c, Muscles of Syrinx; mu, 

 Muscles (after Owen). 



though, in the relative position of the vibrating mem- 

 branes thus set edge to edge, it is, as far as I know, 

 unlike every instrument commonly used. There are 

 three varieties of syrinx, distinguished by their different 

 positions in the trachea or bronchi, but I shall describe 

 only the one which is by far the most common. 



Near to the point where the windpipe divides to form 



