610 STRUCTUEE AND CLASSIFICATION OF BIRDS 



but some considerable modification of the last tracheal and 

 early bronchial rings. The last four tracheal rings are 

 soldered together to form a cartilaginous box, which behind 

 and in front shows no Hnes of demarcation between the 

 several rings of which it is composed. There is a membrana 



Fig, 241 Tracheal Pouch op Emu cut open (aetek Mukie). 



Tv Tv' the poLicli : flp, opening into trachea ; c.(^.s, prolongation of upper end of pouch ; 

 ■^' fh, fV, fibrous glands. 



tympaniformis and a pessulus ; the first three or four 

 bronchial semi-rings are different from those which follow. 

 The remaining Eatitse have no distinct syrinx. In Struthio, 

 for example (see figs. 43, 44, p. 64), although there is a mem- 

 brana tympaniformis completing the bronchi internally, there 

 is neither pessulus nor intrinsic muscles. The syrinx of 

 Apteryx is about on the same level. Casuarius is rather 



