LAWS OF BONE ARCHITECTURE 259 



great importance in determining the mechanical strength of this 

 part of the femur. Transverse sections affoi'd the most accurate 

 means of com])uting the strengtli of the bone at various sections. 

 In Part III the mechanical analysis of these separate sections 

 has been made, and the results are presented in table 5. Figure 

 20 gives in diagrammatic form the strength of the femur about 

 its two principal axes A- A and B-B. 



The shaft of the femur 



The shaft will be considered here as that portion of the femur 

 h'ing between the lower limit of the lesser trochanter and the 

 distal 6 inches of the femur. 



1. Frontal sections. The shaft consists of a thick, hollow, 

 cylindrical shell of compact bone with relatively unimportant 

 short, thick trabeculae projecting from the inner surface of the 

 shaft. The central core of the shaft is occupied by ver}^ fragile 

 trabeculae which support the marrow in this cavity, but which 

 probably do not normally affect the strength of the femur. 



The frontal longitudinal sections of the shaft, being cut through 

 a more or less circular hollow cylinder, do not give an adequate 

 picture of the structure because large variations occur in the 

 form of the sections as they are taken at a distance from the 

 center. Figure 24 gives a general idea of the structure of the 

 shaft, but the most accurate representation of the shaft is given 

 by the serial transverse sections, shown in Plates 1-3. 



Figure 24 clearly shows the gradual fusion of the trabeculae 

 in the head and neck to form the shaft, and at the lower end the 

 gradual thinning of the shaft which takes place with a corre- 

 sponding increase in the amount of spongy bone. 



2. Sagittal sections. Longitudinal sagittal sections of the shaft 

 proper are somewhat similar in general appearance to the frontal 

 sections, as they are cut in the longitudinal plane at right 

 angles to the frontal sections. But they give only a general idea 

 of the structure of the shaft, as they become distorted as they 

 are taken in planes away from the center. 



3. Serial transverse sections. These sections through the shaft 

 are shown in Plates 1-3 (sections 20-52). They give the detailed 



