and more powerfully up to F, F[#] [Illustration: musical
notation] the natural transition from the thick to the thin register, as
well in the _male_ as in the _female_. The voicebox is perceptibly lower
in all the tones of the thick register than in quiet breathing."

I confess my inability to understand how the vocal ligaments can get
_longer_ by relaxing and _shorter_ by stretching. But apart from this I
assert that there is no relaxing of the vocal ligaments at the break
between the Lower Thick and the Upper Thick at all. This is clearly
proved by the ring-shield aperture, which would open immediately if such
were the case. I also doubt whether the action or inaction of the
pyramids determines the break between the Lower Thick and the Upper
Thick, as they are cartilages--_i.e._, pieces of gristle--and cannot,
therefore, by any vibrations of their own assist in the production of
tone. The tension of the vocal ligaments increases as we sing up the
scale until the ring-shield aperture has quite disappeared. But while it
remains so closed, and without the vocal ligaments being any further
stretched, we can yet sing higher still. The gradations of tone are now
no longer formed by the action of the ring-shield muscles (see p. 34),
but by the shield-pyramid muscles which press the vocal ligaments more
and more closely together, until at last scarcely any trace of a slit
remains between them. Another result of this action of the
shield-pyramid muscles must also be to narrow the space _below_ the
vocal chink, which, as we know from the experiments of J. Mueller, has
the effect of raising the pitch of tones. I think it very likely,
therefore, that the change from the lower to the upper thick is really
brought about by the shield-pyramid muscles coming into play after the
ring-shield muscles have done their share.

THE THIN REGISTER.

"All the tones of the thin register are produced by vibrations only of
the fine, inner, slender edges of the vocal ligaments. In this action
the vocal ligaments are not so near together, but allow of a fine linear
space between them, and the pocket ligaments are pressed further back
than in the production of the tones of the thick register. The rest of
the action of the glottis is, however, entirely the same. With the
beginning of the thin register at F[#] [Illustration: musical notation]
the whole vocal chink appears again longer, and the vocal ligaments are
much looser than in the highest t