246
ON SOUND.
In the ordinary state of ease, the vocal ligaments are
not stretched longitudinally with any special force, and
the ends of the right ligament and those of the left
ligament are not pressed together. There are, in fact,
special muscles for separating them, which in the state
of personal ease appear to be in action, effecting that
separation. The opening is then sufficiently wide to
allow the breath to pass very freely ; and the ligaments,
in their unstretched state, will not vibrate.
For producing sound, other muscles are brought into
play, namely, 1st, muscles which press together (but
probably not close together) the ends of the two liga¬
ments: 2nd, muscles which extend each ligament to any
arbitrary degree of tension.
In this state, when air is forced from the lungs
through the glottis, necessarily passing with great
rapidity (as the chink is now very narrow), it puts the
ligaments into vibration, sufficiently rapid to produce a
musical note. The pitch of the precise note produced
will depend on the tension given to the ligaments. So
that, for utterance of a musical sound, two systems of
muscular action are required. One, consequent on the
volition “to utter a musical sound” is that of drawing
close together the right ligament and the left ligament ;
the other, consequent on the volition “to utter a musical
sound of a particular pitch,” is that of stretching the
ligaments to a definite tension.
This action may be imitated experimentally in
various ways, of which we quote, as probably the easiest