510 STRUCTURE 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 lines of demarcation between the 

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



FIG. 241. TRACHEAL POUCH OF EMU CUT OPEN (AFTER MURIE). 



Tp, Tp 1 , the pouch ; ap, opening into trachea ; c.rf.s, prolongation of upper end of pouch ; 



/&, /&', fibrous glands. 



tympaniformis and a pessulus ; the first three or four 

 bronchial semi-rings are different from those which follow. 

 The remaining Batitse 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 



