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The motions of points on its anterior wall on either side 
of the breast bone may take place in an upward, forward, 
and lateral direction, and a stethometer has been con- 
structed by means of which these movements may be 
measured during any one act of breathing, in three planes 
at right angles to one another. 
From the records obtained with this instrument it has 
been observed that the ratio of the forward to the upward 
and outward movements varies very greatly, not only in 
different individuals but in the same person, and that by 
the constraining influence of the will it is possible to cause 
at one time the forward and at another the upward motion 
to predominate. 
The upper ribs have sometimes more forward movement 
than the lower ; in childhood its extent is very large, but 
with the advance of age the movement in this plane be- 
comes comparatively very small. In disease the ratios of 
the motions in the three planes are much altered — especially 
in the early stages of consumption and in pleurisy after the 
effusion has been absorbed. 
By means of an instrument for ascertaining the angles 
made by the plane of the rib-circuits with the vertical it 
may be demonstrated mathematically-- 
1. That the upward dimensions of the movements of the 
anterior ends of the ribs are sufficiently accounted for by the 
upward rise of the ribs, their chordlengths being taken as 
radii, their vertebral attachments as centres. 
2. The outward indications are also probably to be 
accounted for by the radial rise of the costal cartilages, the 
sternal articulations being taken as centres. 
8. But from the above-mentioned observations it is obvious 
that the forward thrust of the anterior ends of the ribs can- 
not be accounted for by their simple rise from a more to a 
less oblique position. From the records of the chest move- 
ments it appears that there is no constant relation to be 
