12 PASSERES. 



ihe classification of the Passeres as witness the TracJieophonce. 

 Briefly three types of syrinx are recognized the Tracheo- 

 bronchial, the Tracheal and the Bronchial, the last two being 

 derivatives of the first. The tracheo-bronchial is the type found 

 in the Oscines and Sub-Oscines. Herein the lower end of the 

 trachea has the last four or five rings welded to form a little dice- 

 shaped box communicating below with the bronchi. The 

 bronchial rings I and II are closely attached to this box, 

 while III forms a strong arcuate bar supporting a delicate 

 sheet of membrane stretched between rings I and II on the 

 one hand and IV on the other. The bronchial rings are in- 

 complete on their inner aspects, their free ends supporting a 

 " tympanic membrane," which plays an important part in voice 



Syrinx of a Magpie, showing the Diacromyodian attachment of the intrinsic 

 muscles at the ends of the bronchial semi-rings. The left-hand figure is a side 

 view and the right-hand figure a dorsal view of the syrinx. The membranous 

 parts between the bronchial semi-rings and the internal tjmpaniform membrane 

 are dotted ; II, III are the second and third bronchial semi-rings; T.i, the 

 internal tympaniforin membrane ; st, the muscle from the side of the trachea 

 to the upper end of the clavicle; 1, 2, 3, 4, 5, 6, the syringeal muscles ; there 

 is a 7th, which is hidden by the Oth ; the 4th is hidden below and between the 

 1st, 2nd, and 3rd. 



production. At the junction of the bronchi with the trachea is a 

 bony bar the " pessulus." This supports a thin fold of mem- 

 brane whose free edge cuts across the bottom of the dice-shaped 

 box of the trachea! tube. By its vibrations it acts like the " free 

 reed " of an organ-pipe. Muscular lips extending from the 

 inner surfaces of bronchial semi-ring III narrow the aperture on 

 either side of the "reed" during the production of the " voice" 

 or song, and thus complete the mechanism of voice production. 

 In the Tracheal syrinx a variable number of the lower tracheal 



