LAWS OF BONE ARCHITECTURE 255 



B. Lateral (tensile) system of trabeculae. As the compact 

 bone of the outer portion of the shaft approaches the greater 

 trochanter it gradually decreases in thickness. Beginning at a 

 point about 1 inch below the level of the lower border of the 

 greater trochanter, numerous thin trabeculae are given off from 

 the outer portion of the shaft. These trabeculae lie in three 

 distinct groups: one (c) which rises from the upper part of the 

 shaft and passes almost vertically and ends in the surface of the 

 greater trochanter: the second (d) which rises lower in the 

 shaft than the group just mentioned, making an angle of 30 to 

 45 degrees with the shaft, and crosses in almost parallel curved 

 lines the neck of the femur and ends in the medial surface of 

 the head of the femur: the third (e), which rises from the same 

 side of the shaft and below group (d) and crosses the longitu- 

 dinal axis of the femur and ends in the medial side of the neck 

 and shaft. 



c. The greater trochanter group. These trabeculae rise from 

 the outer part of the shaft just below the greater trochanter and 

 rise in thin, curving lines to cross the region of the greater tro- 

 chanter and end in its upper surface. Some of these filaments are 

 poorly defined. This group intersects the trabeculae of group 

 a which rise from the opposite side. The trabeculae of this group 

 evidently carry small stresses as is shown by their slenderness. 



d. The principal tensile group. This group springs from the 

 outer part of the shaft immediately below group c, and curves 

 convexly upward and inward in nearly parallel lines across the 

 neck of the femur and ends in the inferior portion of the head. 

 These trabeculae are somewhat thinner and more widely spaced 

 than those of the principal compressive group (b). All the 

 trabeculae of this group cross those of groups a and b at right 

 angles. This group is the most important of the lateral system 

 (tensile) and, as will be shown later, the greatest tensile stresses 

 of the upper femur are carried by the trabeculae of this group. 



e. The secondary tensile group. This group consists of the 

 trabeculae which spring from the outer side of the shaft and lie 

 below those of the preceding group. They curve upward and 

 medially across the axis of the femur and end more or less irreg- 



