For singer or speaker, the correct use of the breathing apparatus determines the question of success or failure; for without mastery of the motive power all else is unavailing. For a voice user, therefore, the first requisite is a well-developed chest, the second, complete control of it. It must not be supposed that a singer's breathing is something strange or complex, for it is nothing more than _an amplification of normal, healthy breathing_. In contrast, however, to the undisciplined casual breathing of the general public, the singer is a professional breather. THE MUSCLES OF RESPIRATION There are two sets of respiratory muscles, one for inspiration and another for expiration,--twenty-two or more in all. The principal muscles of inspiration are the diaphragm and the intercostal muscles that elevate the ribs. The chief muscles of expiration are the four sets of abdominal muscles and the intercostal muscles that depress the ribs. The diaphragm is _not_ a muscle of _expiration_. THE DIAPHRAGM The diaphragm is in form like an inverted bowl (Fig. 8). It forms the floor of the thorax (chest) and the roof of the abdomen. It is attached by a strong tendon to the spinal column behind, and to the walls of the thorax at its lowest part, which is below the ribs. In front its attachment is to the cartilage at the pit of the stomach. It also connects with the transverse abdominal muscle. The diaphragm being convex, in inspiration the contraction of its fibres flattens it downward and presses down the organs in the abdomen, thus increasing the depth of the thorax. Expiration depends wholly on other muscles. [Illustration: FIGURE 8.] The muscles so far mentioned are all that need "conscious education;" the others will act with them voluntarily, automatically. The abdominal muscles relax during inspiration and the diaphragm relaxes during expiration, thus rendering the forces nearly equal, though the strength is in favor of the expiratory muscles. This is what is needed, for the breath while speaking or singing must go out under much greater tension than is necessary for inhalation. Inspiration should be as free as possible from obstruction when singing or speaking. Expiration must be under _controlled_ pressure. THE LUNGS The lungs are spongy bodies which have no activity of their own beyond a little elasticity. They are controlled by the muscles of respiration. Figure 8 shows the organs of the body in their natural positions. The diaphragm is relaxed and curved upward, as in expiration. During inspiration the diaphragm is drawn down until it lies nearly flat. INSPIRATION