British medical journal . of exact mathematical treatment; mathematicianswould call it a statically iudetei-minate structure. By making one or two legitimate assumptions, resultsat least qualitative may be simply deduced. The foot maybe considered replaced by a simple structure like anunsymmetrical roof truss (see Fig. 1): a b and a g repre-sent the anterior and posterior limbs of the pedal arch,and B c is the tie of the truss which may bo regarded asthe resultant of the various ligaments and muscles whichhave a similar function in the foot. The points b and crepresent, of course, the centres
British medical journal . of exact mathematical treatment; mathematicianswould call it a statically iudetei-minate structure. By making one or two legitimate assumptions, resultsat least qualitative may be simply deduced. The foot maybe considered replaced by a simple structure like anunsymmetrical roof truss (see Fig. 1): a b and a g repre-sent the anterior and posterior limbs of the pedal arch,and B c is the tie of the truss which may bo regarded asthe resultant of the various ligaments and muscles whichhave a similar function in the foot. The points b and crepresent, of course, the centres of pressure under the toesand heel respectively. Thus we replace the foot, with itsnumerous bones, muscles, and ligaments, by a virtual archor truss supported against collapse by a virtual tie. _ It isnow a matter of simple statics to calculate tho variationof tension in bc as the heel of the truss is raised orlowered. The downward force at a is, of course, regardedas a constant and proportional to the weight of the In the first place there .are two limiting positions of thefoot to be considered—tho one, entirely supposititious,when the toes are raised until the posterior limb a c of thearch becomes vertical, the other, a case exemplified bymany professional dancers, when the heel is raised so thatthe anterior limb a b becomes vertical. In both of theseextreme positions there is no tension in the virtual tie ofthe arch. For any intermediate position there is a tensionin B c, and the variation of this is shown graphically inFig. 2. The abscissae of points on tho curve iu Fig. 2represent in degrees the inclination of the sole of the fuotto the horizontal; the angle of inclination being positivewhen the heel is higher than the toe and negative whenlower. The ordinates of the curve represent the tensionsin the virtual tie at the various angles of inclination. Thescale of the ordinates is clearly quite immaterial, since thoabsolute tension is jJroportional to the weight of t
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectmedicine, bookyear185
