THE ANATOMY OF BIHD-SONG. 110 



tain touch of picturesque melody. Even the 

 woodpeckers, notably ErythrocepTialus and 

 Colaptes, have very pure fife-notes. 



But let us now turn and examine the true 

 mouth of the avian flute. 



VI. 



The upper end of a song-bird's trachea is 

 peculiarly modified, terminating in a chink 

 or slit just at the root of the tongue. This 

 slit, the glottis, is surrounded by a bundle of 

 muscles, and has two heavy lips by which it 

 is closed at the bird's will. The anterior por- 

 tion of the glottis aperture is nearly circular, 

 but it terminates posteriorly in a thin angle, 

 like a keen knife-cut. Out of this little chink 

 has been blown the rapturous sylvan fluting 

 about which the poets have raved since the 

 days of Homer and Sappho. 



Just in front of the glotfcidian fissure there 

 is a valve-like fold of mucous membrane 

 which, when the tongue is raised, is drawn 

 across the anterior line of the circular part of 

 the opening. This modified upper end of the 

 trachea, the so-called larynx, is connected 

 with the tongue-bone by slender muscles, and 

 the lips of the fissure are moved by nicely 

 adjusted intrinsic muscles, of which the mock- 

 ing-bird has five pairs. The contractor mus- 

 cles of the trachea are connected with the 

 larynx, and when they are drawn taut the 

 glottis is depressed between the horns of the 

 hyoid bone, which helps to form a resonant 

 cavity in the bird's mouth, and at the same 

 time the anterior fold of mucous membrane 

 is erected as a sort of sounding-board in front 

 of the orifice, while the tongue acts as a re- 

 flector or vibrator, as the need may be. In 

 the mocking-bird and, indeed, in nearly all 

 the true song-birds that I have dissected, the 

 air cells, "jiiembranous pneumatic sacs," are 



