PSITTACI 25.> 



single, or double on the neck, and where it widens out 011 

 either side of the carina sterni a strongly feathered lateral 

 branch is given off. 



The variations shown in the pterylosis are not great. 

 They concern the more or less definite separation of the 

 lateral ventral tract and the slighter or more pronounced fea- 

 thering of the anterior end of the posterior dorsal Y. Thus 

 in Lathanuts and Platycercus the lateral ventral tracts are 

 well marked, and the posterior fork of the dorsal tract does 

 not diminish much in width where it comes into contact 

 with the anterior fork. In Trickoglossus the exact reverse 

 of these conditions obtains, the lateral ventral tracts being but 

 obscurely delimited from the main tract, and the dorsal tracts 

 of the hinder part of the body almost ceasing before their 

 junction with the anterior half. 



PsepJiotus, Cyanorhamphus, Pyrrhulopsis,Agapornis, &c., 

 agree with Platycercus. In Ara the outer branch of the 

 pectoral tract is not definitely separable, but the dorsal tracts 

 are more like those of Platycercus. Conurus is much the 

 same. 



The syrinx of the Psittaci ! seems to show two main 

 varieties. 



a. In the following species there is a syrinx of the type 

 which will be described immediately : 



Cacatua cristata. 



,, triton. 



Philippinarum. 

 Microglossa aterrima. 

 Calyptorliynclms Banks i. 

 String ops habroptilus. 



The syrinx is in these species remarkable for the fact that 

 the first semi-rings of the bronchi are weak and cartilaginous, 

 and are usually separated from each other by considerable 

 tracts of membrane. Cacatua itself represents the most ex- 



1 The syrinx has been chiefly studied by GIEBEL, ' Zur Anatomic der 

 Papageien,' Zcitschr. f. d. ges. Wiss. xix. p. 133, and by PARSONS and myself, 

 ' On certain Points in the Anatomy of Parrots,' Ac., P. Z. S. 1893, p. 507. 



