THE ANATOMY OF BIRD-SONG. 115 



do with the relative yalues of the notes. I 

 have seen a mocking-bird with its chin resting 

 upon its breast run the full compass of its 

 voice ; whilst, on the other hand, it is not un- 

 common for it to ut ter every note it has 

 mastered, with its neck at full stretch. Such 

 feats are possible on account of the exceeding 

 elasticity of the walls of the posterior mouth- 

 cavity and the anterior throat-cavity. The 

 shortening of the trachea really does this : it 

 gives the lungs greater power to act directly 

 upon the glottis, thus adding volume to the 

 notes. For instance, if you watch a quail as 

 it whistles " Bob White," you will note that 

 its head moves up and down with the length- 

 ening And shortening of the trachea necessary 

 to the extremes of power required. The yel- 

 low-billed cuckoo, muttering its well-known 

 croak, slightly elevates its beak, and you can 

 see its upper throat palpitating in accord with 

 the rattling notes. Indeed, it appears to be 

 sucking the sounds back from the glottis into 

 the hollow of the mouth and throat, where 

 they are shaken about like peas in a box ! 

 All the common song-birds have a way of ut- 

 tering falsetto notes occasionally. The most 

 notable example of this is the nocturn of the 

 mocking-bird, in which falsetto phrases are 

 used with singularly plaintive and touching 

 effect. After careful study, I have concluded 

 that the notes above described are produced 

 by a division of the vibrating air-column in the 

 mouth, caused by the bird drawing its tongue 

 back nearly over the glottis, while the man- 

 dibles are kept as nearly closed as possible. 

 The brown thrush is expert in rendering very 

 delicate falsetto sketches, and watching him 

 with a strong field-glass has convinced me 

 that I have correctly described his method. 

 The caged mocking-bird rarely indulges in 

 this delicious music and therefore is iard to 



