LAWS OF BONE ARCHITECTURE 241 



equivalent area of compact bone. These results are shown in 

 diagrammatic form for the entire length of the femur in figure 

 17. In figure 18a the axial unit-stress is shown to scale for 

 section 8, due to the load of 100 pounds on the femur-head. 

 Table 6, Column 2 gives the numerical value of the axial load, 

 and Column 5 the corresponding axial unit-stresses for the 

 whole femur. 



B. Unit-stresses due to bending moment. As has been ex- 

 plained in Part II (26-4^) in the discussion of beams, the effect 

 of bending moment is to cause tensile stresses on one side 

 of the neutral axis and compressive stresses on the opposite 

 side. The amount of this unit-stress depends upon the distance 

 of the fibers considered from the neutral axis. These stresses are 

 proportional to the distance from the neutral plane, and are 

 zero at this plane. Hence the maximum unit-stresses due to 

 bending moment will be in the outermost fibers of any given 

 section. 



By the application of the formula (Part II, 39), s = Mc/I, 

 the A'alue of the maximum unit-stress due to bending moment 

 can be readily computed for the sections analyzed. The \'alue 

 of M, the bending moment, for successive sections is given 

 graphically in figure 16 and numerically in table 6. The value 

 of c, the distance from the neutral plane to the outermost fiber, 

 and of / the moment of inertia of the cross section are given in 

 table 5, table of properties of femur sections. In figure 18a the 

 stresses due to the bending moment are shown for section 8. 

 A similar diagram could be constructed for all the other sections 

 analyzed. 



In figure 17 curves 3 and 4 show graphically the values of the 

 maximum unit-stresses, tensile and compressive, due to the 

 bending moments produced by a load of 100 pounds on the 

 femur. 



C. Horizontal and vertical shearing unit-stresses. The aver- 

 age vertical shearing unit-stress at each section is derived by 

 dividing the vertical shear at the section by the net area of 

 compact bone of the section. Then the actual horizontal shear- 

 ing unit-stress is computed by multiplying this average shear- 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 21, NO. 2 



