waves.

THE LARYNX

*The Sound-producing Mechanism of the Body* consists of the following
parts:

1. Delicately arranged bodies that are easily set in vibration.

2. An arrangement for supplying the necessary force for making these
bodies vibrate.

3. Contrivances for modifying the vibrating parts so as to produce changes
in pitch and intensity.

4. Parts that reenforce the vibrations.

5. Organs by means of which the sounds are converted into the forms of
speech.

The central organ in this complex mechanism is

*The Larynx.*--The larynx forms a part of the air passages, being a short
tube at the upper end of the trachea. Mucous membrane lines the inside of
it and muscles cover most of the outer surface. The framework is made of
cartilage. At the top it is partly encircled by a small bone (the hyoid),
and its opening into the pharynx is guarded by a flexible lid, called the
_epiglottis_. The cartilage in its walls is in eight separate pieces, but
the greater portion of the structure is formed of two pieces only. These
are known as the _thyroid cartilage_ and the _cricoid cartilage_ (Fig.
149). Both can be felt in the throat--the thyroid as the projection known
as "Adam's apple," and the cricoid as a broad ring just below.

[Fig. 149]

Fig. 149--The larynx.--_A._ Outside view. _B._ Vertical section through
larynx, showing inside. 1. Thyroid cartilage. 2. Cricoid cartilage. 3.
Trachea. 4. Hyoid bone. 5. Epiglottis. 6. Vocal cord. 7. False vocal cord.
8. Lining of mucous membrane.

The _thyroid cartilage_ consists of two V-shaped pieces, one on either
side of the larynx, meeting at their points in front, and each terminating
at the back in an upward and a downward projection. Between the back
portions of the thyroid is a space equal to about one third of the
circumference of the larynx. This is occupied by the greater portion of
the _cricoid cartilage_. This cartilage has the general shape of a signet
ring and is so placed that the part corresponding to the signet fits into
the thyroid space, while the ring portion encircles the larynx just below
the thyroid. Muscles and connective tissue pass from the thyroid to the
cricoid cartilage at all places, save one on each side, where the downward
projections of the thyroid form hinge joints with the cricoid. These
joints permit of motion of either cartilage upon the other.

At the summit of the