408 



ON THE PETRELS COLLECTED DURING 



Zoo}. Cfcall. 

 Exp. vol. iv. 

 pt. xi. p. 38. 



Ibid. p. 39. 



Hid. p. 40. 



the posterior ends of the second semi-rings, and all ultimately fusing into 

 the pessularbox of the adult. In Puffinus obscurus there is a complete 



Fig. 22. 



Syrinx of Bulweria macgillivrayi, from before. 

 Fig. 23. 



The same, from behind. 



pessular bar, formed by the third bronchial rings. There is no pessular 

 box, the bronchial rings being all free from each other. 



In (Estrelata lessoni (figs. 27, 28, p. 410) the syrinx becomes much more 

 specialized and ossified. The fifth bronchial rings are strong and curved, 

 and to these are attached, by fan-shaped insertions of tendon, the vocal 

 muscles. The five preceding rings (which must therefore be the last 

 tracheal and first four bronchial) are narrow, closely united, and ossified 

 over a rhomboidal space in the middle line anteriorly. Behind there is 

 a pessular box formed by these rings, and the four preceding tracheal ones 

 in addition, the first two of these having a median patch of ossification. 

 There is a well-developed and ossified pessular bar. 



(Estrelata mollis is quite similar, except that the box is composed of 

 one ring less.* 



* I regret not having as yet been able to examine any adult bird of (Estrelata brevi- 

 rosfris, all my specimens being young and consequently with the tracheal rings un- 

 ossified and 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. 



