70 STEUCTURE AND CLASSIFICATION OF BIRDS 



is contained in a paper upon the general anatomy of this 

 bird by Gabrod.' 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 

 afiinity. As to the Passeres, it is, as Furbeingee 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 

 ' ' On some Poin-ts in the Anatomy of Steaiomis,' P. Z. S. 1873, p. 526. 



