456 ON THE NOSTRILS OF THE CORMORANT. 



succeeds in forcing a passage into the nasal cavity. If the skin 

 ■which forms the outer boundary of the slit is carefully reflexed, 

 a groove is exposed which runa from the external slit-like nostril 

 to a narrow canal lined apparently by modified mucous mem- 

 brane. This canal, when the mucous membrane remains, is 

 externally from \\ to 2 millim. in diameter ; but it rapidly 

 diminishes, and appears to end blindly. In all the specimens 

 examined, however, when the skin has been reflexed, it is possible to 

 pass through this canal, without forming a false passage, a bristle 

 about the size of an ordinary horse-hair, i. e. less than 1 millim. 

 in diameter. The bristle is more easily passed in young birds 

 than in old ones : this seems to be due to the osseous canal being 

 relatively larger than in the former. Almost immediately beyond 

 this narrow passage is the large nasal chamber, lying above and 

 internal to the palatine bone, and in free communication with the 

 buccal cavity. The mucous membrane lining the nasal chamber 

 has the same structure and the same nerve-supply as in other 

 aquatic birds. 



The nasal region of the Cormorant, and to some extent also in 

 the Gannet (Sula), thus differs chiefly from the nasal arrangement 

 in other birds : — 1st, in having a very small external nostril, the 

 passage in this slit-like aperture being almost obliterated ; 2nd, 

 in having the osseous canal only lg to 2 millim. in diameter 

 externally, and scarcely 1| millim. at its narrowest part ; and 

 3rd, in having the nasal chamber in very free communication 

 with the mouth. 



This state of things, it may be presumed, explains the gaping 

 of the bill, in the case of the Cormorant, to obtain air needful to 

 sustain the increased activity of respiration which is produced by 

 the exertion of prolonged flight. 



