TRACHEA OF THE ROOK. 23 



of the thyroid bone, a, by two slender elastic ligaments, e e. 

 The space between the outer edge of the arytenoid bones, d d, 

 and the edge of the thyroid bone, a, and its appendages, h J, 

 is filled up by the raucous membrane internally, and by muscles 

 to be presently described. Along the upper edge of each ary- 

 tenoid bone, d d, is placed a thin cartilage, f f. The two 

 first rings of the trachea, g g, are incomplete. 



It may here be stated that, although in man and the quadru- 

 peds, in which this part is proportionally larger and more com- 

 plex, the voice with all its varieties as to intensity, is produced by 

 the muscles and membranous cords of the larynx; yet in birds it 

 is produced at the lower extremity of the windpipe, the syrinx^ 

 Fig. 1, q, but is modulated by the larjmx so as to be formed into 

 notes. If we take the trachea of a Rook or Blackbird, and 

 blow through its two bronchi, we cause a sound having some 

 resemblance to the cry of the bird ; but this experiment does 

 not disclose to us the part in which the sound is produced. 

 Let us therefore cut the trachea across in the middle. By 

 blowing into the upper part we cause no sound, but by blow- 

 ing into the bronchi, we produce the same sound as before ; 

 and if we remove the tracheal and bronchial rings, until no- 

 thing is left but the syrinx and two or three of the rings, still 

 the sound, though feebler, is heard. The trachea has been cut 

 across in the living bird, and its anterior half closed, and yet 

 the bird has emitted a cry somewhat similar to its natural one, 

 although it could not fashion it into notes. In the human 

 larynx, the tocal cords, which vibrate under the impulse of the 

 air, and thus produce sound, are placed in the larynx ; but in 

 birds there are no traces of them there, and this is the reason, 

 or a reason, why in them sound is not produced in the larynx. 

 It is in the vicinity of the lower larynx, or sifrinx, as I have 

 called it, that the vibrating membrane is placed, as I shall 

 presently shew. 



One of the best trachea? for the purpose of experimenting 

 upon, is that of the Wild Swan, when in a recent state. In 

 February and March 1838, when I had four specimens, I had 

 one removed from its attachments. On introducing the bronchi 

 into my mouth, and blowing hard into them, I produced a dull 



