VI FORM AND FUNCTION 137 
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, 
Fic. 34.—Syrinx. 
Raven, A with bronchi; a, b, c, half-rings ; where the two bronchi face each other 
there is nothing but membrane. _ 8, side view ; the outer part of the lower end of the 
trachea and of the nearer bronchus being cut away ; mM, Membranous inner wall of 
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 cdge, it is, as far as I know, 
unlike every instrument commonly used. There are 
three varicties 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 
