LAWS OF BONE ARCHITECTURE 237 



sections 6, 8, 10, etc. to 17 by the lines JL, JM, JN, JO, JP, 

 JQ and JR, respectively. The vertical shearing forces at the 

 same successive sections are represented in the same figure by 

 the lines FL, FM, FN, FO, FP, FQ, and FR, respectively. After 

 section 17 is passed the character of the vertical shearing force 

 is reversed, but its amount is so small as to be negligible. 



The amounts of these axial and shearing forces are shown in 

 figure 16, in diagrammatic form for the whole length of the 

 femur. Table 6 (cols. 2 and 4) gives the numerical values of 

 these axial and vertical shearing forces. 



3. Bending moment. In addition to the axial loads and the 

 vertical shears, the load on the femur-head produces a tendency 

 to cause bending in the femur. In accordance with the defini- 

 tion previously given (Part II, 26), the amount of the bend- 

 ing moment is the product of the force acting on the section 

 by the perpendiculai' distance from the point to the line of 

 action of the force. The line of action of the force is AB (fig, 

 14) and its amount W, is 100 pounds, which remains a con- 

 stant for the whole length of the femur. Hence, the bending 

 moment at successive points will be proportional to the perpen- 

 dicular distance from the given point (on the neutral axis) to 

 AB. The numerical values of the bending moment at succes- 

 sive sections are given in table 6 (col. 3), and in figure 16 these 

 values are shown in diagrammatic form (p. 240). 



It will be noted that the bending moment rapidly increases 

 in the head and neck of the femur to reach a maximum between 

 sections 16 and 18. Beyond the latter section the amount of 

 the bending moment diminishes almost uniformly to zero just 

 below section 75. 



4- Vertical and horizontal shear. As a fundamental principle 

 in mechanics, it may be stated that at any point in any beam 

 the horizontal shearing force is equal to the vertical shearing 

 force at the same point. The intensity of the horizontal shear- 

 ing force, in any transverse section, varies from a minimum 

 at the fibers most distant from the neutral axis to a maximum 

 in the neutral plane (Part II, 50, 51), the variations depending 

 upon the shape of the cross section. Hence it will be neces- 



