nt of the glottal
lips "presumably occurs by nervously aroused contractions of the fibers
of the muscles in the glottal lips." Continuing, Prof. Scripture says:

"Physiologically stated, the action for a vowel is as follows: Each
glottal lip consists mainly of a mass of muscles supported at the ends
and along the lateral side. It bears no resemblance to a membrane or a
string. The two lips come together at their front ends, but diverge to
the rear. The rear ends are attached to the arytenoid cartilages. When
the ends are brought together by rotation of these arytenoid cartilages,
the medial surfaces touch. At the same time they are stretched by the
action of the crico-thyroid muscles, which pull apart the points of
support at the ends.

"In this way the two masses of muscle close the air passage. To produce
a vowel such a relation of air pressure and glottal tension is arranged
that the air from the trachea bursts the muscles apart for a moment,
after which they close again; the release of the puff of air reduces the
pressure in the trachea and they remain closed until the pressure is
again sufficient to burst them apart. With appropriate adjustments of
the laryngeal muscles and air pressure this is kept up indefinitely,
and a series of puffs from the larynx is produced. The glottal lips open
partly by yielding sidewise,--that is, they are compressed,--and partly
by being shoved upward and outward. The form of the puff, sharp or
smooth, is determined by the way in which the glottal lips yield; the
mode of yielding depends on the way in which the separate fibers of the
muscles are contracted.

"These puffs act on the vocal cavity, that is, on a complicated system
of cavities (trachea, larynx, pharynx, mouth, nose) with variable
shapes, sizes, and openings. The effect of the puffs on each element of
the vocal cavity is double: first, to arouse in it a vibration with a
period depending on the cavity; second, to force on it a vibration of
the same period as that of the set of puffs. The prevalence of one of
the factors over the other depends on the form of the puff, the walls of
the cavities, etc."

Prof. Scripture does not undertake to point out a difference between the
correct vocal action in tone-production, and any incorrect action. This
difference in action does not seem capable of definition by any
analysis of the acoustic principles involved.

_Mechanical Principles of the Vocal Action_

In Part II, Chapter II