REPORT ON THE ANATOMY OF THE PETRELS. 



35 



and second united ; the others are incomplete, inturned anteriorly, and not co-ossified 

 to form a box. There is a good pessulus borne by the last tracheal. 



Fig. 11. — Syrinx of Prion vitiaius, from before. 



Fig. 12. — The same, from behind. 



In Pagodroma (figs. 13, 14) the four first bronchial semi-rings are ossified and firmly 

 united into a bony box behind ; anteriorly, however, the first and fourth bronchial rings 

 axe free, whilst on one side the second and third are quite fused both before and behind. 



The last tracheal ring is free throughout. 



Fig. 13. — Syrinx of Pagodroma nivca, from before. 



Fig. 14. — The same, from behind. 



Daption much resembles Pagodroma, there being a bony box, formed however by 

 the fusion of the first three bronchials with the last tracheal ring. In neither of these 

 genera is there any trace of a tracheal septum. 



It is by a further development of the syrinx of Pagodroma that the peculiar one of 

 the Fulmars is formed. 



In Thalassceca glacialoides (figs. 15, 16) the last two tracheal rings are ossified and 

 fused together anteriorly, a median descending process being developed which lies 



