OF MOVEMENTS OF CHEST-WALL IN RESPIRATION. 257 



of the rib considered as a rigid body must necessarily pos- 

 sess the following attributes : — 



i . It must approximate to a segment of a circle. 



2. It will be the same in its ascent and descent. 



3. Its shape for the same rib will always be nearly the 

 same. 



4. Its curve will depend (a) upon the angle formed by 

 the plane of the rib-circuit with the perpendicular, 

 and (b) upon the length of the radius, the chord- 

 length of the rib employed. 



It is hardly needful to point out that the first and second 

 of these characteristics are not found in the actual curves 

 described by healthy ribs ; and, in order to test the third 

 and fourth, an attempt was made to ascertain what influence 

 could be exerted upon the movement by the constraining 

 power of the will. In figs. 3 and 4 the result is given in 



one case (3) of an effort to raise the rib with but little 

 forward motion, and (4) to push its end forward without 

 raising it. 



Although the tracing is irregular from the constraint 

 put upon the ordinary motion, it is evident that in No. 3 

 we have a closer approximation to the simple radial move- 

 ment ; and in No. 4 the effort has succeeded in producing 

 1*2 inch of forward push with only 0'6 inch of rise. 



These peculiarities of the motions of the rib in health 

 SER. III. vol. v. s 



