TUBINAKES 



44!) 



structure. In Garrodia the first three bronchial rings are 



O 



complete. In Thalassoeca glacialoides the last four tracheal 

 rings are incomplete behind, and are quite like the four 

 succeeding bronchial semi-rings, being, moreover, like them, 



-75 



FIG. 211. SKULL OF Diomedea cxulans 



(AFTER HUXLEY). 

 Vo, vomer ; ?,fxp, maxillo palatines ; 1't, pterygoid. 



FIG. 212. SKULL OK Procellaria 

 girjantea (AFTER HUXLEY). 



PI, palatines ; *, basipterygoid process. 

 Other letters as iu fig. 211. 



ossified. This modification is carried to its furthest extreme 

 in Ossifraga. In this petrel the last nine or ten tracheal 

 rings are incomplete in front, and the last twelve or so are 

 incomplete behind. Thus the membrana tympaniformis 

 does not commence for some distance away from the bifur- 

 cation of the respiratory tube, the rings being double and 



G G- 



