270 JOHN C. KOCH 



i(>lati\('ly at a considerable distance^ from the neutral axis. It is 

 evident that the hollow shaft provides efficiently for resisting 

 hendins moment not only due to the load on the femur-head, 

 but from any other loads tending to produce bending in other 

 planes. 



3. Economy for resisting axial stress. The relatively small 

 axial stress, which is compressive at all points in the femur and 

 is uniformly distributed over the area of each cross section, is 

 efficiently provided for by the compact bone of the shaft, as 

 may be seen by reference to figure 18 and 18 « and table 6. 



4. Conclusions. From the foregoing it may be concluded that: 



1. The inner architecture of the shaft is adapted to resist in 

 the most efficient manner the combined action of the minimal 

 shearing forces and the axial and maximum bending stresses. 



2. The structure of the shaft is such as to secure great strength 

 with a relatively small amount of material. 



Significance of the inner architecture of the distal part of the femur 



1. Relation between structure and function. The function of 

 the lower end of the femur is to transmit through a hinged joint 

 the loads carried by the femur. For stability the width of bear- 

 ing on which the hinge action occurs should be relatively large. 

 For economy of material the expansion of the end bearing should 

 be as lightly constructed as is consistent with proper strength. 

 In accordance with the principles of mechanics already discussed, 

 the most efficient manner in which stresses are transmitted is by 

 the arrangement of the resisting material in lines parallel to the 

 direction in which the stresses occur and in the paths taken by 

 the stresses. Theoretically the most efficient manner to attain 

 these objects would be to prolong the innermost filaments of 

 bone as straight lines parallel to the longitudinal axis of the 

 bone, and gradually to flare the outer shell of compact bone out- 

 ward, and continuing to give off filaments of bone parallel to 

 the longitudinal axis as the distal end of the femur is approached. 

 These filaments should be well-braced transversely and each 

 should carry its proportionate part of the total load, parallel 



