cords, and this is effected by a group of muscles termed the adductors,
which pull on the pyramid cartilages in such a way that the vocal processes
are drawn towards one another in the manner shown in fig. 7. Besides the
abductor and adductor groups of muscles, there is a muscle which acts in
conjunction with the adductor group, and by its attachments to the shield
cartilage above and the ring cartilage below makes tense the vocal cords
(_vide_ fig. 5); it is of interest to note that this muscle has a separate
nerve supply to that of the abductor and adductor muscles.

[Illustration: FIG. 5

Diagram after Testut (modified), showing the larynx from the front.]

[Illustration: FIG. 6

Diagram after Testut (modified), showing the posterior view of the larynx
with the muscles.]

On the top of the pyramid cartilages, in the folds of mucous membrane which
cover the whole inside of the larynx are two little pieces of yellow
elastic cartilage; and in the folds of mucous membrane uniting these
cartilages with the leaf-like lid cartilage (epiglottis) is a thin sheet of
muscle fibres which acts in conjunction with the fibres between the two
pyramid cartilages (_vide_ fig. 8). I must also direct especial attention
to a muscle belonging to the adductor group, which has another important
function especially related to vocalisation: it is sometimes called the
vocal muscle; it runs from the pyramid cartilage to the shield cartilage;
it apparently consists of two portions, an external, which acts with the
lateral ring-shield muscle and helps to approximate the vocal cords; and
another portion situated within the vocal cord itself, which by contracting
shortens the vocal cord and probably allows only the free edge to vibrate;
moreover, when not contracting, by virtue of the perfect elasticity of
muscle the whole thickness of the cord, including this vocal muscle, can be
stretched and thrown into vibration (_vide_ fig. 8). In the production of
chest notes the whole vocal cord is vibrating, the difference in the pitch
depending upon the tension produced by the contraction of the tensor
(ring-shield) muscle. When, however, the change from the lower to the upper
register occurs, as the photographs taken by Dr. French and reproduced in a
lecture at the Royal Institution by Sir Felix Semon show, the vocal cords
become shorter, thicker, and rounder; and this can be explained by
supposing that the inner portion of the vocal muscle contracts