which are imbedded in the mucous membrane, one on each side of the arytenoids. These minor S.P. cartilages doubtless perform some function in steadying and strengthening the action of the laryngeal muscles. 5. The Epiglottis. The epiglottis is

ep.

Soft palate (s.p.) and epiglottis (ep.) during (A) respiration and (B) swallowing. (From Thornton's Human Physiology.)

a leaf-like valve or

lid which in the act

of swallowing closes over the top of the larynx, helping to keep food out to prevent strangulation. It is attached to the

inside of the thyroid

cartilage in front and stands

erect during

respiration and speech, leaving the air passage

open and free.

B. The Glottis.

The glottis (Figs. 8 and 9) is the slit-like

opening into the larynx from above. Its two sides, made up of elastic tissue along the edges of the thyroarytenoid muscles, are the vocal folds (cords or bands). In quiet breathing the glottis is a rather wide triangular

opening (Fig. 9B and B'), and in vocalization the inner edges of the folds are closely drawn together (Fig. 94 and A'). The average length of the vocal bands in the adult male is about of one inch; in the adult female about of one inch.

FIG. 9.-Three Laryngoscopic Views of the Superior Aperture of the Larynx and Surrounding Parts in Different States of the Glottis during Life. (Czermak, from Quain's Anatomy.)

A, the glottis during the emission of a high note in singing; B, in easy inhalation; C, in taking a deep breath; b, base of tongue; e, the upper free part of the glottis; e', the tubercle or cushion of the epiglottis; ph, part of the anterior wall of the pharynx behind the larynx; in the margin of the aryteno-epiglottidean fold; w, the swelling of the membrane caused by the cuneiform cartilage; s, corniculum; a, tip of arytenoid; co, true vocal folds; cus, false vocal folds; tr, trachea; b, bronchi in C. A', B', C', diagrams of the glottis and positions of the arytenoid cartilages in the three states.

C. The False Vocal Folds and the Ventricles. The false vocal folds, the function of which is not known but which is probably the protection of the true vocal folds, are two ridges

of tissue directly above the true vocal folds. Just between the false folds and the true folds, the walls of the larynx are indented, forming the ventricles, the only function of which seems to be to provide room in which the vocal folds may move as they vibrate.

D. The Hyoid Bone. The hyoid bone (Fig. 5a), sometimes called the tongue bone, roughly resembles a horseshoe in shape and is situated about one inch above the top of the thyroid cartilage in such a way as to furnish the upper attachments for the ligaments and muscles which support the larynx proper. The hyoid bone is also important in furnishing the attachments for the muscles which control the rear portion of the tongue. The hyoid bone is the one bone in the body not articulated with the rest of the skeleton.

E. The Muscles of the Larynx. The muscles of the larynx are divided into two groups called intrinsic muscles and extrinsic muscles. The former move the several cartilages of the larynx with relation to each other, while the latter depress and elevate the larynx as a whole.

1. Intrinsic Muscles. a. Crico-thyroid. The crico-thyroid is a large muscle attached to the two cartilages indicated by the name. Its action pulls the cricoid and the thyroid together in front. This increases the distance between the vocal processes of the arytenoids and the inner front surface of the thyroid, and thus tenses the vocal folds.

b. Thyro-arytenoids. The thyro-arytenoid muscles are a pair of muscles attached to the front and inner surface of the thyroid cartilage and to the vocal processes of the arytenoid cartilages. The cartilaginous inner edges of these muscles are the vocal folds themselves. The tensing of these muscles relaxes the folds.

c. The lateral crico-arytenoids. The lateral crico-arytenoids are so situated between the cricoid and arytenoid cartilages that their pull rotates the arytenoid cartilages inward, bringing the vocal folds together and tensing them, thus closing the glottis.

d. The posterior crico-arytenoids. The posterior cricoarytenoids are attached to the cricoid and arytenoid cartilages in such a way that by their contraction the arytenoid cartilages

10

--11

13

FIG. 10. Muscles of the Tongue, Pharynx, etc., of the left side. (Allen Thomson, from Quain's Anatomy.)

a, external pterygoid plate; b, styloid process; c, section of lower jaw; d, hyoid bone; e, thyroid cartilage; f, cricoid cartilage; between d and e, the thyro-hyoid membrane; g, isthmus of thyroid body; 1, stylo-glossus muscle; 2, stylo-hyoid; 3, stylo-pharyngeus; 5, genio-hyoid; 6, genio-glossus; 7, hyo-glossus; 8, lingualis inferior; 9, part of superior constrictor of pharynx; 10, back part of middle constrictor; 11, inferior constrictor; 12, upper part of esophagus; 13, crico-thyroid muscle.

are rotated outward, the vocal folds are moved apart at the rear and relaxed, thus opening the glottis.

e. The arytenoid muscle. The arytenoid muscle, situated between the two arytenoid cartilages, works with the lateral

crico-arytenoids in pulling the two arytenoid cartilages together, thus aiding in closing the glottis.

2. Extrinsic Muscles. In addition to the intrinsic muscles of the larynx, there are two rather important extrinsic muscles. These are the sterno-thyroid and the thyro-hyoid.

a. The sterno-thyroid. The sterno-thyroid, as its name implies, is attached to the thyroid cartilage and to the sternum or breast bone. Its action is to pull the whole larynx downward. When this muscle contracts it exerts a pressure upon the thyroid gland, through which comes the blood supply of the larynx. The action of the sterno-thyroid muscle as it depresses the whole larynx may be a factor in causing a depression of the epiglottis. This action probably has a muffling effect upon the deep low tones and may be in some measure responsible for the guttural and pectoral qualities which we shall discuss in the chapter on vocal quality.

—

b. The thyro-hyoid. The hyoid bone (Fig. 10) is held in place by various muscles attached to portions of the skull. This hyoid bone is suspended by muscular connections with the skull, and largely through the agency of this thyro-hyoid muscle, the larynx is suspended from the hyoid bone. When this muscle contracts, the larynx is pulled upward. It is easy to observe this action in swallowing.

We have, then, in the intrinsic and extrinsic musculature of the larynx, a relatively simple mechanism which is capable of a practically infinite number of adjustments. The cricothyroid muscle pulls the front portion of the cricoid cartilage and the front portion of the thyroid cartilage together, thus tipping back the arytenoid cartilages to which the posterior ends of the vocal folds are attached. This is probably the principal mechanism for tensing the vocal folds. The action of the other intrinsic muscles, as has been shown, is to move the vocal folds together and to draw them apart again, thus opening and closing the glottis. The vocal folds are themselves the edges of muscles and in a sense act to relax them

4 This is really a pair of muscles, one on each side of the thyroid cartilage.