[Description: FIG 3.--Diagram after Barth to illustrate the changes in the diaphragm, the chest, and abdomen in ordinary inspiration _b-b_', and expiration _a-a_', and in voluntary inspiration _d-d_' and expiration _c-c_', for vocalisation In normal breathing the position of the chest and abdomen in inspiration and expiration is represented respectively by the lines _b_ and _a_; the position of the diaphragm is represented by _b_' and _a_'. In breathing for vocalisation the position of the chest and abdomen is represented by the lines _d_ and _e_, and the diaphragm by _d_' and _c_'; it will be observed that in voluntary costal breathing _d-d_ the expansion of the chest is much greater and also the diaphragm _d_' sinks deeper, but by the contraction of the abdominal muscles the protrusion of the belly wall _d_ is much less than in normal breathing _b_.] A glance at the diagram (fig. 3) shows the changes in the shape of the thorax in normal subconscious automatic breathing, and the changes in the voluntary conscious breathing of vocalisation. It will be observed that there are marked differences: when voluntary control is exercised, the expansion of the chest is greater in all directions; moreover, by voluntary conscious effort the contraction of the chest is much greater in all directions; the result is that a larger amount of air can be taken into the bellows and a larger amount expelled. The mind can therefore bring into play at will more muscular forces, and so control and regulate those forces as to produce infinite variations in the pressure of the air in the sound-pipe of the vocal instrument. But the forces which tend to contract the chest and drive the air out of the lungs would be ineffective if there were not simultaneously the power of closing the sound-pipe; this we shall see is accomplished by the synergic action of the muscles which make tense and approximate the vocal cords. Although the elastic recoil of the lungs and the structure of the expanded thorax is the main force employed in normal breathing and to some extent in vocalisation (for it keeps up a constant steady pressure), the mind, by exercising control over the continuance of elevation of the ribs and contraction of the abdominal muscles, regulates the force of the expiratory blast of air so as to employ the bellows most efficiently in vocalisation. Not only does the contraction of the abdominal muscles permit of control over the expulsion of the air, but by fixing the cartilages of the lowest six ribs it prevents the diaphragm drawing them upwards and _inwards_ (_vide_ fig. 2). The greatest expansion is just above the waistband (_vide_ fig. 3). We are not conscious of the contraction of the diaphragm; we are conscious of the position of the walls of the chest and abdomen; the messages the mind receives relating to the amount of air in the bellows at our disposal come from sensations derived from the structures forming the wall of the chest and abdomen, viz.