114 THE ANATOMY OF BIRD-SONG. 



stirred the air of Arcady, or trembled in the 

 vineyards of old Provence. 



But bird-song cannot have its mystery 

 wholly solved by dissection. The parts of the 

 organs are so extremely minute and so ob- 

 scure in their connection and correlation that 

 we must turn to extrinsic and general obser- 

 vations for assistance* in interpreting their 

 functions. With this view, let us go watch 

 a mocking-bird while he sings. 



IV. 



Everybody has noticed how a singing bird 

 expands and compresses its throat just below 

 and between the prongs of the lower mandible 

 during the utterance of its musical phrases. 

 When the notes are keen and shrill, the throat 

 is drawn close, and when a grave passage is 

 blown, the throat is puffed out like that of a 

 toad. This puffing process is not merely a 

 lengthening of the trachea (or tracheal column 

 of air), as Prof. Huxley would have us be- 

 lieve it is ; it is more. The posterior cavity of 

 the mouth is greatly expanded laterally, ver- 

 tically, and longitudinally, so as to form a 

 hollow drum behind the glottis. Into this 

 chamber (lined with tightly drawn mem- 

 branes) the breath from the glottis is reflect- 

 ed by the tongue and the anterior part of the 

 roof of the mouth; there its vibrations are 

 communicated to the largest possible column 

 of air, sounding the gravest notes of the bird's 

 voice. When the throat is compressed, this 

 drum or chamber is reduced to the minimum, 

 and the vibrant column of air gives forth the 

 sharpest sounds possible to the organ. 



Observe the mocking-bird or the brown 

 thrush, as it sings 



" Of summer in full-throated ease," 

 and you will see that the lengthening or short- 

 ening of the tracheal column has but little to 



