172 JAY ARTHUR MYERS 



reaching its dorsal wall. The second, enumerated caudad from 

 the tympanum, are somewhat broader and extend farther dor- 

 sad. The first and the second cartilages are often fused for a 

 part of their course. The third intermediate syringeal cartilages 

 differ from the second only in being slightly broader. The 

 fourth and the last of this series present more striking differ- 

 ences. They are larger than any of the preceding ones. Their 

 free dorsal extremities lie laterad of the dorsal pyramid and 

 gradually become very broad, but their medio-lateral diameter 

 is not increased. These cartilages are arched slightly cephalad. 



Caudad to the intermediate syringeal cartilages are the 

 bronchial half-rings (fig. 4). The first of these differ from the 

 typical half-rings in the following respects : first, they are longer 

 and have much greater diameters; second, both ends are attached 

 to the pessulus; third, well marked caudal prolongations extend 

 from their ventral extremities and connect them with the 

 second half -rings; fourth, their ventral extremities in old indi- 

 viduals become ossified; fifth, they are arched, with their con- 

 vexities pointing caudad. . 



Between the first half-rings and the last intermediate car- 

 tilages are very large, somewhat oval-shaped spaces, the upper 

 thirds of which are directly opposite to the pessulus (fig. 4). 



The second half-rings, which are somewhat smaller than 

 the first, have enlarged ventral extremities which are attached 

 to the cartilaginous prolongations of the first half-rings mentioned 

 above. Their dorsal extremities are free. 



The third bronchial half-rings are quite similar to the typical 

 half -rings which lie caudad to. them. The only noticeable 

 modification is an enlargement of their ventral extremities. 

 They are somewhat flattened bands of cartilage which are free 

 at both ends. 



b. Vibrating membranes. Certain parts of the highly modified 

 skeleton, just described, serve as attachments for specialized 

 semitransparent membranes, which are the real voice producing 

 elements. Two pairs of these are present in the chicken. They 

 are known as the external and the internal tympanic membranes. 

 Another membrane, not strictly a vibrating membrane, will also 

 be discussed under this heading. 



