STEGANOPODES 407 



which are fused and ossified where they pass into it ; in 

 front the last of these and the next following are ossified and 

 fused in the middle line ; the middle one of the three is con- 

 tinuous with the pessulus. 



P. m it rat ux chiefly differs in the larger number of rings with 

 which the broad three-way piece comes into contact in front 

 and in the greater length of the membrana tympaniformis. 



P. fuscus is remarkable for the degree in which the 

 syrinx is flattened from before backwards. This is caused 

 by the straightening of two of the bronchial semi-rings, 

 which thus come, though hardly longer than the others, to 

 project out considerably beyond them. At a first glance 

 these two semi-rings appear to be the first two of the bron- 

 chial series which are commonly among birds different from 

 those which follow. There are, however, five pairs of bars 

 in front of them, only separated in the middle line in front 

 by a furrow ; on slitting up the windpipe it may be observed 

 that there is really a septum' between them, and that they 

 are bronchial. Owing to the peculiar form of the sixth and 

 seventh semi-rings the membrana tympaniformis is exposed 

 behind, but not in front. 



P. ouoc ratal /(* and P. crispns have syringes which are 

 very much alike. When removed from the body, at any 

 rate, the bronchi stand out at right angles to the trachea. 

 This is due to the very large posterior end of the pessulus, 

 which is broadened into a bar at right angles to and longer 

 than the median portion of the pessulus. It is not ossified. 

 There is a slight dilatation of each bronchus, which is carried 

 to an excess in the next species. 



In P. rufescens the characters of the syrinx of the last 

 species are carried to an extreme. The pessulus is the same 

 in shape, but ossified. The bronchi are greatly swollen for 

 the space of about an inch, there being occasionally some 

 forking and anastomosing of the individual rings. The ends 

 of the rings in the swollen region are nearly in contact, being- 

 separated only by a narrow membranous interval. 



In Fregata aqaila the syrinx has a pair of intrinsic 

 muscles and the bronchidesmus is incomplete. The syrinx 



