70 STRUCTURE AND CLASSIFICATION OF BIRDS 



is contained in a paper upon the general anatomy of this 

 bird by GARROD. 1 From that paper we borrow the descrip- 

 tion as well as the illustration. It will be seen from that 

 drawing (fig. 48) that the trachea of the bird bifurcates, as 

 does the trachea of a mammal, without any modification of 

 the rings, either tracheal or bronchial. The latter are at first 

 complete rings ; it is not until the thirteenth or fourteenth 

 the exact position appears to vary that the syrinx appears ; 

 here the rings cease to be complete rings, and are semi-rings- , 

 their inner ends being completed by membrane, the mem- 

 brana tympaniformis. To the first of these modified semi- 

 rings is attached in the case of either bronchus the intrinsic 

 muscle of the syrinx. 



The transition between this purely bronchial syrinx and 

 the more usual tracheo-bronchial syrinx is afforded by 

 various genera of cuckoos and goatsuckers (of which a par- 

 ticular description will be found later), in which the mem- 

 brana tympaniformis is placed, as in Steatornis, far down 

 the bronchus, but which have also a sheet of membrane 

 forming a continuation of the membrana upwards to the 

 trachea, which is due to the non-closure internally of the 

 earlier bronchial semi-rings ; this latter gets more and more 

 limited in various genera until we have the purely tracheo- 

 bronchial syrinx, in which the wide membrana tympani- 

 formis commences at once on the bifurcation of the 

 bronchi. 



The syrinx has undoubtedly some value as a test of 

 affinity. As to the Passeres, it is, as FURBRINGER has 

 remarked, a ' classical ' object for the determination of 

 relationships. In other families too it is of importance. From 

 a more general standpoint, however, apparently but little 

 reliance can be placed on the modifications of this so variable 

 organ. An approximation to the reptilian condition in the 

 absence of any special modification at the bifurcation of the 

 bronchi is seen in some of the struthious birds and in the 

 American vultures. It is not clear, however, that this 

 simplicity is not a case of the reduction rather than of the 



1 ' On some Points in the Anatomy of ,S7w/omis,' P. Z. ,V. 1873, p. 526. 



