LAWS OF BONE ARCHITECTURE 251 



of the femur. These divisions differ very markedly in struc- 

 ture, and the principles of mechanics involved in each require 

 separate consideration. 



The inner architecture of the upper femur 



1. Serial frontal longitudinal sections. The sections are cut 

 in planes parallel to the plane passing through the longitudinal 

 axis of the shaft and the head and neck of the femur, which is 

 directed medially and about 12 degrees anterior to the true 

 frontal plane of the body. 



Figure 21 and figure 28 represent such a section cut through 

 the central part of the femur and very close to the longitudinal 

 axis of this bone. Comparison of this figure with those showing 

 the parallel sections adjacent to it shows a very close similarity 

 of the inner architecture of all these sections. For this reason 

 the detailed description given for the mid-section shown in figure 

 21 will also apply to the others. 



Referring to this figure, it is seen that the spongy bone of 

 the upper femur is composed of two distinct systems of tra- 

 beculae arranged in curved paths: one, which has its origin in 

 the medial (inner) side of the shaft and curving upward in a fan- 

 like radiation to the opposite side of the bone; the other, having 

 its origin in the lateral (outer) portion of the shaft and arching 

 upward and medially to end in the upper surface of the greater 

 trochanter, neck and head. These two systems intersect each 

 other at right angles. The spaces between these intersecting 

 systems of filaments are of variable size and shape, depending 

 upon their position. In the head of the femur these spaces are 

 very small and in the lower portion of the section they are of 

 much greater size. The two systems of trabeculae will now be 

 discussed in detail. 



A. Medial (compressive) system of trabeculae. As the com- 

 pact bone of the medial (inner) part of the shaft nears the head 

 of the femur it gradually becomes thinner and finally reaches the 

 articular surface of the head as a very thin layer. From a 

 point at about the lower level of the lesser trochanter, 2^ to 3 

 inches from the lower limit of the articular surface of the head, 



