256 STRUCTURE AND CLASSIFICATION OF BIRDS 



treme type ; in Cacatua cristata, for example, when the syrinx 

 is seen on a lateral view the membrane occupies a great deal 

 of the outer lateral region of the commencement of the 

 bronchus. 



The semi-rings of the bronchus are at first very small, and 

 do not extend across the side of the bronchus ; they gradu- 

 ally increase in length, until at the sixth or seventh they 

 come to extend right across the syrinx. In Microglossa 

 aterrima the syrinx is in certain respects less abnormal ; 

 the rings are still feeble, but on a lateral view of the organ 

 they extend completely across, and there is on such a 

 view no bare tract of membrane, such as we have figured 

 in Cacatua. 



Calyptorhynchus Banksi is intermediate between the 

 two extremes ; the first semi-ring only is incomplete, inas- 

 much as it does not reach from one side of the syrinx to 

 the other or rather we should say from the anterior to the 

 posterior side. 



String ops habroptilns has the same weak cartilaginous 

 bronchial semi-rings ; but on a lateral view of the syrinx they 

 are seen to extend right across. 



b. The second group contains the following genera :- 



Chrysotis. Tanygnathus. 



Pyrrhulopsis. Eos. 



Triehoglossus. Poly teles. 



Lorius. Platycercus. 



Pionus. Pceocephalus. 

 Psittacus. 



These genera' are differentiated from those of the first 

 division by the fact that the bronchial semi-rings are as a rule 

 ossified, and are frequently more or less fused together ; at 

 the same time the first ring is commonly concave upwards, 

 whereas in the parrots of the first-mentioned group the 

 bronchial semi-rings are straight. 



The most extreme type is perhaps offered by Chrysotis; 

 of this genus I have seen the following species : 



