nges,
one at the bottom and the other at the top of the windpipe. Dr.
Garrett seems not to have been aware of this fact.

The vocal ligaments in the adult male are, in a state of rest, about
three-quarters of an inch long, and in the female about half an inch. I
pointed out before that the vocal ligaments are attached in front to the
shield (pl. VII, 6) and behind to the pyramids (pl. VII, 3, 3). Let it
now be borne in mind--1st, That the pyramids, in their turn, are
fastened to the upper border of the ring cartilage; and 2nd, That by
drawing the shield downwards and forwards upon the ring, the distance
between the upper border of the ring (pl. VII, 5) and the front of the
shield (pl. VII, 6) is increased, and it will be easily seen that this
movement must of necessity have the effect of stretching the vocal
ligaments.

This drawing of the shield downwards and forwards upon the ring is
brought about by a pair of muscles ascending on either side, in the
shape of a fan, from the ring to the shield cartilage (pl. VIII, 1, 2).
These muscles we name the "Ring-Shield Muscles." In opposition to them
there is another pair inside the shield, running parallel with the vocal
ligaments (pl. IX, 1, 2, 3). They are attached (like the vocal
ligaments) in front to the shield cartilage and behind to the pyramids.
These muscles we will call the "Shield-Pyramid Muscles." They counteract
the ring-shield muscles, and having overcome their resistance, pull the
shield cartilage up again, thereby, of course, relaxing the vocal
ligaments. The ring-shield muscles, therefore, _stretch_ the vocal
ligaments and the shield-pyramid muscles _relax_ them. The
shield-pyramid muscles have an additional function--that of pressing
together the vocal ligaments, under certain circumstances, thereby
narrowing the opening between them. They have therefore been, in these
later days, called the Sphincter[G] muscle of the glottis. They have
also been called the Vocal Muscles, since they play so important a part
in the formation of all vocal tone that a paralysis of them causes total
loss of voice.

[Illustration: PLATE VIII.

SIDE VIEW OF THE VOICEBOX, OR LARYNX.

1, 2. RING-SHIELD MUSCLE (CRICO-THYROIDEUS).

3. LID.

4. SHIELD.

5, 6. UPPER HORNS OF THE SHIELD.

7. RING.

8. WINDPIPE.
]

[Illustration: PLATE IX.

SIDE VIEW OF THE VOICEBOX, OR LARYNX, SHOWING THE INTERIOR OF THE LEFT
HALF.

1, 2, 3. SHIELD-PYRAMID MUSCLE (THYRO-ARYT