tion. Inspiration is then essentially an active muscular process, whereas expiration is typically, although not always, a passive process carried on principally by what physiologists call the "elastic recoil." Inspiration and expiration together constitute respiration. (Fig. 3.)

B. The Muscles. We are now ready to examine the musculature which produces respiration. As we have already seen, most of the active muscular process in respiration is connected with the enlargement of the thorax and the consequent inrush of air. In breathing for speech, we frequently have to use more muscular action in expiration than is necessary in breathing for vital purposes only.

1. The Intercostals. There are three sets of muscles which control the action of the ribs in breathing. They are (1) the scaleni, (2) the intercostals, and (3) the elevators of the ribs. The principal ones are the intercostals. Thornton says:2

"The scaleni muscles pass from processes of the cervical vertebrae to the first two ribs, and by their action raise or at least fix these ribs. The external intercostals whose fibres run downwards and forwards in the spaces between the ribs so act, when the two first pair of ribs are fixed by the scaleni, that the ribs are elevated both in front and at the sides, moving on their articulations with the vertebrae. As they slant downwards, the ribs when raised must thrust the sternum forward and enlarge the antero-posterior diameter of the chest; and since they form arches which increase in sweep, at least from the first to the seventh, the elevation of one into the place of another causes the chest to become wider from side to side. Further as the ribs are raised there is some stretching of the costal cartilages and a certain amount of rotation of the ribs which brings their outer surfaces more directly outwards, these effects plainly aiding the enlargement of the thoracic cavity."

Thornton explains that the contraction of the elevators of the ribs also increases the size of the chest cavity.

* John Thornton, Human Physiology, p. 137.

2. The Diaphragm. This is the principal muscle used in breathing. It is an arched, tendinous-muscular sheet which forms the floor of the chest cavity and the roof of the abdominal cavity. It is attached to the sternum and the ribs

FIG. 4.The Lower Half of the Thorax, with four Lumbar Vertebrae, showing the Diaphragm from before. (Allen Thomson, after Luschka. From Quain's Anatomy.) a, sixth dorsal vertebra; b, fourth lumbar vertebra; c, ensiform process; d, d', aorta, passing through its opening in the diaphragm; e, oesophagus; f, opening in the tendon of the diaphragm for the inferior vena cava; 1, central, 2, right, and 3, left division of the trefoil tendon of the diaphragm; 4, right, and 5, left costal part, ascending from the ribs to the margins of the tendon; 6, right, and 7, left crus; 8 to 8', on the right side, the sixth, seventh, and eighth internal intercostal muscles, deficient towards the vertebral column, where in the two upper spaces the levatores costarum and the external intercostal muscles 9, 9, are seen; 10, 10, on the left side, subcostal muscles.

in front, to the ribs at the sides and the rear, and to the spinal column itself. In its relaxed position it is domelike in shape, and when it contracts it merely becomes slightly less dome

like. As it contracts it increases the vertical diameter of the chest considerably, presses down upon the viscera contained in the abdomen, and thus causes the muscular walls of the abdomen to bulge out. When the diaphragm and the intercostal muscles relax, the diaphragm ascends and the ribs fall. back into place, largely through the action of the costal cartilages between the ribs which have been stretched during inspiration. The abdominal muscles may push the viscera up against the diaphragm and thus aid in the forced expiration which is frequently necessary in speech. The abdominal muscles may also pull down the lower ribs. The central importance of the diaphragm in breathing has been recognized since the days of the Greeks, who called the principal nerve which controls the action of the diaphragm the "phrenic" or "soul" nerve because they observed that when this nerve is cut death is the immediate consequence.

C. Breathing in Vocalization. We have already indicated that there are some differences between normal breathing and breathing in vocalization. Some of the contrasts are in the rate of respiration, which is usually speeded up3 during vocalization, in the amount of air inspired, which is usually somewhat greater, and, most strikingly, in the ratio between the time consumed in inspiration and expiration; expiration being prolonged in speech, whereas in normal breathing it takes about the same length of time as inspiration. The rate of normal quiet respiration in the adult is from 6 to 20 times per minute, depending upon various physiological factors, one of the most important of which is the rate of metabolism (the rate at which bodily tissues break down and are repaired). All muscular action affects the process of respiration. Since vocalization is a matter of muscular action, it inevitably affects the process of respiration.

3 The exact reverse of this is frequently asserted. But recent experimentation in the speech laboratory at the University of Wisconsin convinces us that respiration is speeded up rather than slowed down during vocalization. This is also true even in silent reading.

II. THE LARYNX

The larynx, or voice box, is the organ in which the vocal vibrations are initiated. It is a structure made up principally

of a number of cartilages and the muscles which control their action. (Figs. 5a and 5b.)

A. The Cartilages. 1. The Cricoid Cartilage. The cricoid cartilage is situated on, and attached to, the top ring of

the trachea (Fig. 5a). Its name literally translated means signet ring; the broad part of the ring is at the back and the narrow part in front. This cartilage is slightly movable.

2. The Thyroid Cartilage. Mounted upon the cricoid cartilage is the thyroid cartilage (Figs. 5a and 56), the largest cartilage of the larynx, which derives its name from a word meaning buckler or shield. The vocal folds are attached to the inner surface of the front of the thyroid cartilage, directly below the notch which we may feel with the point of the finger. Just above the attachment of the vocal folds, the foot of the epiglottis is inserted into the thyroid cartilage (Fig. 5b).

Thyroid Cartilage

Arytenoid Cartilage

Cricoid Cartilage

Crico-thyroid

axis of rotation

Vocal Fold

Direction of pull of crico-thyroid muscle

FIG. 6. Diagrammatic Vertical Section of Larynx. (From Waller's Introduction to Human Physiology.)

3. The Arytenoid Cartilages. There are two of these arytenoid cartilages (Fig. 5b), so named on account of their resemblance to ladles, which rest upon the top of the cricoid cartilage at the rear. These arytenoid cartilages, while smaller than the cricoid and the thyroid, are of very great importance in speech, because they at their inner basesfurnish the points of attachment for the posterior ends of the vocal folds.

4. The Minor Cartilages. There are two pairs of small cartilages the function of which in voice production is little known. These are the cornicula laryngis or the cartilages of Santorini, which are nodules on the apices of the arytenoids, and the cuneiform cartilages or the cartilages of Wrisberg,