onists of the above-named muscles, and
they may act either very much alone or, to some extent, in cooeperation
with the above, to regulate or steady their action; for in movements
so complicated as those required for voice-production it is highly
probable that we are inclined to reduce our explanations of muscular
action to a simplicity that is excessive, and to appreciate but
inadequately the delicacy and complexity of the mechanism and the
processes involved. It is quite certain that in the production of the
highest tones of a tenor or soprano several muscles cooeperate, and
one, especially, seems to be of great importance in the formation of
such tones, most of all, perhaps, in high sopranos. The muscle
referred to is the thyro-arytenoid already described. It is not only
attached to the two cartilages indicated by its name, but also along
the whole of the external or outer surface of the vocal band. It will
be remembered that practically all the muscles are arranged in pairs,
one on each side of the middle line. The muscle now under
consideration, more, perhaps, than any other, is complex in its
action. Apparently a very few of its fibres may act more or less
independently of all the others at a particular moment and with a
specific and very delicate result, a very slight change in pitch.
Exactly how this is attained no one has as yet adequately explained;
but it is doubtful whether any singer who does not possess a perfect
control over this muscle can produce the highest tones of the soprano
with ease and effectiveness. It is especially the muscle of the human
birds of the higher flights.

(_b_) To these thyro-arytenoids, which for most singers and all
speakers are probably chiefly relaxing in action, must be added as
aiding in this function another pair, the _lateral crico-arytenoids_.
They are situated between the cricoid and arytenoid cartilages, and
the direction of action is obliquely from below and forward, upward,
and backward, so that the arytenoids are brought forward and also
approximated more or less, which involves relaxed tension, at least,
possibly also shortening of the vocal bands.

When a tenor or soprano singer reaches the upper tones, say about
[Illustration: e'' f'' g''], or higher, there is considerable closing
up in the larynx, much in the way in which the parts of the month are
brought together in sucking. This is termed _sphincter action_, the
mouth and the eyes being closed by such action,