at the break
from the lower to the upper register (_vide_ fig. 11); and that as a result
only the free edges of the cords vibrate, causing a change in the quality
of the tone. As the scale is ascended the photographs show that the cords
become longer and tenser, which we may presume is due to the continued
action of the tensor muscle. Another explanation is possible, viz. that in
the lower register the two edges of the vocal cords are comparatively thick
strings. When the break occurs, owing to the contraction of the inner
portion of the vocal muscle, we have a transformation into thin strings, at
first short, but as the pitch of the note rises, the thin string formed by
the edge of the vocal cord is stretched and made longer by the tensor. It
should be mentioned that Aikin and many other good authorities do not hold
this view.

[Illustration: FIG. 7 A-A', Ring cartilage. B, Shield cartilage. 1, Pyramid
cartilage. 2, Vocal process, with 2', its position after contraction of
muscle. 3, Postero-external base of pyramid, giving attachment to abductor
and adductor muscles at rest, with 3', its new position after contraction
of the muscles. 4, Centre of movement of the pyramid cartilage. 5, The
vocal cords at rest. 5', Their new position after contraction of the
abductor and adductor muscles, respectively seen in I and II. 6, The
interligamentous, with 7, the intercartilaginous chink of the glottis. 8,
The arrow indicating respectively in I and II the action of the abductor
and adductor in opening and closing the glottis.]

[Description: FIG. 7.--Diagram after Testut (modified), showing: (i.) the
action of the abductor muscle upon the pyramid cartilages in separating the
vocal cords; (ii.) the action of the adductor muscles in approximating the
vocal cords.]

[Illustration: FIG. 8]

[Description: FIG. 8.--Diagram after Testut (modified) with hinder portion
of larynx and windpipe cut away, showing the conical cavity of the
sound-pipe below the vocal cords. The ventricle above the vocal cords is
seen with the surface sloping upwards towards the mid line.]

A diagram showing a vertical section through the middle of the larynx at
right angles to the vocal cords shows some important facts in connection
with the mechanism of this portion of the vocal instrument (_vide_ fig. 8).
It will be observed that the sound-pipe just beneath the membranous reed
assumes the form of a cone, thus the expired air is driven like a wedge
again