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 [!-- pagenumber --]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 [!-- pagenumber --](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. the position of the ribs, their degree of elevation and forward protrusion combined with the feeling that the ribs are falling back into the position of rest; besides there is the feeling that the abdominal muscles can contract no more—a feeling which should never be allowed to arise before we become conscious of the necessity of replenishing the supply of air. This should [!-- pagenumber --]be effected by quickly drawing in air through the nostrils without apparent effort and to as full extent as opportunity offers between the phrases. By intelligence and perseverance the guiding sense which informs the singer of the amount of air at his disposal, and when and how it should be replenished and voluntarily used, is of fundamental importance to good vocalisation. Collar-bone breathing is deprecated by some authorities, but I see no reason why the apices of the lungs should not be expanded, and seeing the frequency with which tubercle occurs in this region, it might by improving the circulation and nutrition be even beneficial. The proper mode of breathing comes almost natural to some individuals; to others it requires patient cultivation under a teacher who understands the art of singing and the importance of the correct methods of breathing.
The more powerfully the abdominal muscles contract the laxer must become the diaphragm muscle; and by the law of the reciprocal innervation of antagonistic muscles it is probable that with the augmented innervation currents to the expiratory centre of the medulla there is a corresponding inhibition of the innervation currents to the inspiratory centre (vide [fig. 18], page [101]). [!-- pagenumber --]These centres in the medulla preside over the centres in the spinal cord which are in direct relation to the inspiratory and expiratory muscles. It is, however, probable that there is a direct relation between the brain and the spinal nerve centres which control the costal and abdominal muscles independently of the respiratory centres of the medulla oblongata (vide [fig. 18]). The best method of breathing is that which is most natural; there should not be a protruded abdomen on the one hand, nor an unduly inflated chest on the other hand; the maximum expansion should involve the lower part of the chest and the uppermost part of the abdomen on a level of an inch or more below the tip of the breastbone; the expansion of the ribs should be maintained as long as possible. In short phrases the movement may be limited to an ascent of the diaphragm, over which we have not the same control as we have of the elevation of the ribs; but it is better to reserve the costal air, over which we have more voluntary control, for maintaining a continuous pressure and for varying the pressure.
II. THE REED
I will now pass on to the consideration of the voice-box, or larynx, containing the reed portion of the vocal instrument.
Fig. 4
from Behnke's 'Mechanism of the Human Voice'