Mr. Yarrell on the Organs of Voice in Birds. 317 



and cord-like muscle (d) arises, which goes off to be inserted 

 upon the sternum. The fourth muscle (A) is the shortest of 

 the five, and partly hid by the muscle just described marked /. 

 It arises near the centre of the bottom of the tube, and its 

 fibres, directed obliquely backwards and downwards, 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, oval in shape, 

 and much more fleshy. It has 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 already described, marked e, 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 in- 

 serted upon the extreme end of the first bronchial bone. Fig. 12. 

 represents these five muscles, three of them being partly de- 

 tached for distinction. Should names for these four muscles 

 be considered necessary, they may be called 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 volume 

 of air as well as the force with which it is expelled, while 

 these muscles influence the diameter and length of the bron- 

 chial tubes. 



The advantageous size of the organ of voice in the Raven, 

 and its perfect similarity to those of all the song-birds, was my 

 reason for selecting it in illustration of a subject to which, in 

 quality of tone, there is no resemblance ; but it must not be 

 forgotten that this bird possesses the power of imitating that 

 most diflicult of all sounds, the human voice. 



It will appear anomalous that the Parrots, with their three 



pair of muscles of voice, should possess a greater range of sound, 



♦ or 



