40 



THE VOYAGE OF H.M.S. CHALLENGER. 



(Estrelata mollis is quite similar, except that the box is composed of one ring less. 1 

 In Diomedea brachyura and exulans the calibre of the trachea diminishes very 

 considerably below the place of insertion of the sterno-trac/ica/es. The syrinx (figs. 

 29, 30) is strong and well ossified. The fifth bronchial semi-rings on which end the 

 fanned-out tendinous insertions of the intrinsic muscles are strong and much arched. 

 The four preceding bronchial rings, as well as the last tracheal, are ossified anteriorly 

 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. 



Fig. 29. — Syrinx of Diomedea exulans, from before. 

 About natural size. 



Fig. 30. — The same, from behind. 

 About natural size. 



In Tlialassiarche cidminata (of which I have only examined one) all the five bronchial 

 rings, including the muscular one, are firmly co-ossified together, and free from the 

 rest. There is no complete pessulus, the bony box formed by tne rings terminating 

 posteriorly in a straight and free margin, which a cuneate bar, formed by the inturned 

 anterior ends of the fourth bronchial rings, does not reach. The syrinx of Phcebe1n<i 

 as yet I only know from a young specimen, in which the bronchial rings below the 

 first are incomplete anteriorly, whilst behind there is a box formed by the last two 

 tracheal and first four bronchial rings. 



Majaqueus is very like Diomedea in its syrinx, the penultimate tracheal ring, 

 however, being ossified anteriorly, as well as its five successors, which remain free in 



1 I regret not having as yet been able to examine any adult bird of (Estrelata brevirostris, all my specimens being 

 young and consequently with the tracheal rings vmossified ami generally distinct. There is a box formed by the 

 fusion behind of at least three of the bronchial rings with the last, or two last tracheal ones. The second, third, and 

 fourth bronchial rings are united together anteriorly, the third rings joining the pessular bar. 



