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CORVID.E. 



more obvious by separation. I have called these four mus- 

 cles the long and short, anterior, and posterior tensors : the 

 muscle marked d, from its insertion upon the sternum, may 

 still retain the name of sterno-tracheal. Thus, it will be 

 seen, the lungs govern the quantity of air, as well as the 

 force Avith which it is sent through the trachea, while these 

 muscles influence the diameter, and the length of the bron- 

 chial tubes. The principle upon which the organs of voice in 

 birds is founded, is that Avhich prevails in wind instruments 

 generally ; the notes in the ascending scale being produced 

 by a corresponding contraction of the diameter, or the length 

 of the tube, and vice versa. It may, perhaps, be objected, 

 that the utmost extent of motion which birds appear to have 

 the power of exercising over the different parts of their organ 

 of voice, seems insufficient to account for the effects pro- 

 duced ; but it may in answer be urged, that the closest ex- 

 amination, or most scientific demonstration of the chordae 

 vocales and muscles in man, with all the auxiliary appendages, 

 afford but an imperfect illustration of the varied and extra- 

 ordinary powers of the human voice. 



