

RAVEN. 77 



are inserted by tendon upon the extremity of the first half- 

 circular bone. The fifth muscle, marked g, arises also from 

 the centre of the tube, similar to the last, but is something 

 longer and thicker, having the appearance of being made up 

 of several small muscles in close contact. Its direction is 

 obliquely downwards and forwards, its substance in part 

 hid by the muscle marked 0, and it is attached by a broad 

 base to the last bony ring of the tube, to the cartilaginous 

 projection immediately below, and sends one portion to be 

 inserted upon the extreme end of the first bronchial bone. 

 Figure 4 represents these five muscles, three of them being 

 partly detached to render them more obvious by separation. 

 I have called these four muscles 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 with which it is sent 

 through the trachea, while these muscles influence the 

 diameter, and the length of the bronchial tubes. The 

 principle upon which the organs of voice in birds is founded 

 is that which prevails in wind instruments generally ; 

 the notes in the ascending scale being produced by a cor- 

 responding 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 appen- 

 dages, afford but an imperfect illustration of the varied and 

 extraordinary powers of the human voice. 



