Here is a suitable place to say a few words about how a bird sings. The breath enters and leaves the windpipe through the larynx in the back of the mouth—an organ which, in our throats, contains the vocal cords and voice-producing apparatus; but in birds the larynx is unimportant, for their voice organ is near the lower end of the windpipe, and is called "syrinx" or music box. It consists of an enlargement and modification of the bony rings about the windpipe at the point where it forks into the two branches to the lungs; and incloses vibrating membranes. It is also furnished with small muscles that act to expand or contract the tube and its inner fixtures, thus regulating the column of air forced through the syrinx when the bird calls or sings. These muscles thus control the space and the shape of the opening, and the tension of the membranes that serve as vocal cords. The muscles of the syrinx vary greatly in number and efficiency among birds; and many kinds classed as "singing birds" (Oscines) do not sing melodiously or tunefully because their music box is imperfectly supplied with the proper muscles. They have the instrument, but are unable to play upon it.
