[Illustration: FIG. 2
Adapted from Quain's "Anatomy" by permission of Messrs. Longmans, Green &
Co.]
[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_'.
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