LAWS OF BONE ARCHITECTURE 263 



There is a marked thickening of the shell of bone in the region 

 of the intercondyloid fossa where the anterior and posterior 

 crucial ligaments are attached. This thickened area is about 

 0.4 inch in diameter and consists of compact bone from which a 

 number of thick trabeculae pass at right angles to the main 

 longitudinal system. The inner structure of the bone is here 

 e^'idently adapted to the efficient distribution of the stresses 

 arising from these ligamentary attachments. 



Near the distal end of the femur the longitudinal trabeculae 

 gradually assume cur\'ed paths and end perpendicularly to the 

 articular surface at every point. 



Such a structure is in accordance with the principles of me- 

 chanics, as stresses can be communicated through a frictionless 

 joint only in a direction perpendicular to the joint surface at 

 every point. 



2. Sagittal sections. The sagittal mid-section of the distal 

 portion of the femur is shown in figure 26. It shows two sys- 

 tems of trabeculae, which spring from the anterior and posterior 

 portions of the compact bone of the shaft, which becomes thinner 

 as the joint-surface is approached. Fine trabeculae are given off 

 from the posterior part of the shaft and after crossing the cen- 

 tral area in curving paths and perpendicularly in the anterior 

 articular surface. 



The second system of trabeculae rises from the anterior part 

 of the shaft about 3 inches from the joint, and ends partly on 

 the anterior, but chiefly on the posterior surface of the joint. 

 These trabeculae all end in lines perpendicular to the joint- 

 surface. 



3. Serial cross sections. The serial cross sections from 52 to 

 75, Plates 3 to 5 show the gradual increase in the gross cross 

 sectional area of the femur as the knee-joint is approached. 

 Taken with the longitudinal frontal and sagittal sections already 

 described, these sections give a verj^ clear idea of the internal 

 architecture. Beginning with section 52 the amount of spongy 

 bone gradually increases, but not until section 58 is reached is 

 the entire inner area completely occupied by trabeculae. This 

 corresponds closely with the longitudinal frontal section. As 



