accordingly. Besides, the roof of the bird's mouth is grooved or
convex, and therefore the character of the sounds will be somewhat
dependent upon the position and movement of the upper mandible.

And then there is the bird's tongue, which is constantly in motion
while the musical rehearsal is going on. Throughout its entire length
it can be raised and lowered at the bird's will, or be made to quiver
and roll, and by this means the air column forced up from the lungs is
manipulated in a wonderful way, producing in some cases an almost
unlimited variety of modulation.

Within the bird's neck two elastic tubes run down from the mouth into
the chest. One of them is the gullet or aesophagus, which is the
channel through which the bird's food descends into the crop and
gizzard. The other little cylinder lies in front of the gullet, and is
called the windpipe or trachea, and reaches down to the lungs, which
are the bellows furnishing the wind for the avian pipe organ. As Dr.
Coues says, the trachea is "composed of a series of very numerous
gristly or bony rings connected together by an elastic membrane," and
is supplied with an intricate set of muscles by which it can be
shortened or elongated at the will of the songster himself.

Now let us look at the upper end of this wonderful pneumatic pipe,
which so often throws Pan and all his coterie into a transport when the
thrasher and the wood thrush flute their dithyrambs. Here we find the
larynx. It is simply the anterior specialized portion of the trachea,
located at the base of the tongue, and in mammals is honored as the
voice organ, whereas in birds it is distinguished as the fluting
apparatus, the instrument that really produces the varied vocalization
of the bird realm. But the music is not the product of vocal cords, as
is the case in the human larynx, for at the upper end of the avian
larynx there is a slit or fissure, somewhat elliptical in form, and set
in the fork of the hyoid bone, which constitutes the bifurcated root of
the tongue. This fissure is called the glottis. At the bird's fiat,
it can be opened and closed and made to assume a great variety of
forms. Moreover, just in front of it there is a fold of mucous
membrane called the epiglottis, which is in reality a tiny trapdoor
closing over the opening when necessity requires. When the bird
swallows food or drink, this little flap shuts down, and prevents the
entrance of any clogging substance into