410 



ON THE PETRELS COLLECTED DURING 



Zool. Chall. In Diomedea brachyura and exulans the calibre of the trachea dimi- 



E t XP xi V01 40* n * snes Vei 7 considerably below the place of insertion of the sterno- 



tracheales. The syrinx (figs. 29, 30) is strong and well ossified. The 



fifth bronchial semi-rings, on which end the fanned-out tendinous inser- 



Ibid. p. 39. 



Ibid. p. 40. 



Fig. 27. 



Syrinx of CEstrelafa lessoni, from before. 

 Fig. 28. 



The same, from behind. 



tions of the intrinsic muscles, are strong and much arched. The four 

 preceding bronchial rings, as well as the last tracheal, are ossified ante- 

 riorly and posteriorly, and (with the exception in Diomedea exulans of 

 the fourth bronchial) co-ossified anteriorly into a strong box, with which 

 the penultimate tracheal ring is also connected in the middle line. 

 Behind, the last two tracheal and first bronchial rings are co-ossified, 

 forming a broadly triangular pessular bar or box, whilst one or more (5) 

 of the preceding tracheal rings have patches of ossification mesially. In 

 Thalassiarche culminata (of which I have only examined one) all the five 



