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