JOINT IN A fowl's TONGUE AND ITS VOCAL FUNCTION. 415 



this surface, and in so doing hermetically seals the respiratory 

 slit aforesaid. In other words, the tongue acts as a valve 

 dividing the respiratory tract between the nose and the throat. 

 The movements I have just described as taking place when the 

 beak is open, occur under similar conditions still more readily 

 when it is closed ; for the roof of the mouth is then much 

 nearer the dorsum of the tongue than it is in the other case. 

 If the palatal slit is closed by this means, and the descent of 

 the hyoid begins, the root of the tongue falls with it, but the 

 fore-tongue, owing to the mechanism above explained, can still 

 retain for an instaut its position against the roof of the mouth. 

 The tongue leaves the roof then in two detachments, and at the 

 same time it reopens the sonorous cavity of the mouth, which 

 was practically obliterated by the elevation of the former. Now 

 all these operations, which require many words to describe, take 

 place each time the hyoid bone is raised and depressed ; that is^ 

 coincidently with the emission of a culuck by a broody hen. 

 If the sound is produced, as I believe it to be, at the commence- 

 ment of an in-breath, it suggests an interesting connection with 

 suctional clicks of Dakota and Kaffraria, but that is another 

 story. 



