[Description:  Fig. 2.—­Diagram modified from Quain’s “Anatomy” to show the attachment of the diaphragm by fleshy pillars to the spinal column, to the rib cartilages, and lower end of the breastbone and last rib.  The muscular fibres, intercostals, and elevators of the ribs are seen, and it will be observed that their action would be to rotate and elevate the ribs.  The dome-like shape of the diaphragm is seen, and it can be easily understood that if the central tendon is fixed and the sheet of muscle fibres on either side contracts, the floor of the chest on either side will flatten, allowing the lungs to expand vertically.  The joints of the ribs with the spine can be seen, and the slope of the surface of the ribs is shown, so that when elevation and rotation occur the chest will be increased in diameter laterally.]

[Illustration:  Fig 3]

[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