The vocal tract of an accomplished singer is capable of as many adjustments as a sensitive face is of changes in expression.
The vocal tone in its passage strikes against the walls of the vocal tract.
It is obvious that the tongue also is a highly responsible member of the vocal tract.
When they enter it their vocal tract adjusts itself to it and corresponds with the adjustment employed in it by soprano and tenor.
Alto and bass sing these notes with precisely the same adjustment of the vocal tract.
(an octave lower for male voice) calls for an extraordinary change in the adjustment of the vocal tract.
Some writers class the walls of the pharynx with the solid parts of the vocal tract.
But I do not limit the function of the vocal tract below and above the cords simply to voice quality.