254 



OSTEOLOGY 



Appears at 



4th year ; 



joins body 



about 18th yr. 



Appears at 



Qth month of 



fetal life 



Appears at 

 end of 1st yr. ; 



joins body 

 about 18th yr. 



Appears 13th-14:th 

 year ; joins body 

 about 18th year 



Joins body at 

 20th year 



Lower extremity 



FIG. 252. Plan oi ossification of the femur, 

 five centers. 



From 



0.4 inch in diameter and consists of compact 

 bone from which a number of thick trabeculse 

 pass at right angles to the main longitudinal 

 system. The inner structure of the bone is here 

 evidently adapted to the efficient distribution of 

 the stresses arising from this ligamentary at- 

 tachment. 



"Near the distal end of the femur the longi- 

 tudinal trabecula^ gradually assume curved 

 paths and end perpendicularly to the articular 

 surface at every point. Such a structure is in 

 accordance with the principles of mechanics, 

 as stresses can be communicated through a 

 frictionless joint only in a direction perpendic- 

 ular to the joint surface at every point. 



"With practically no increase in the amount 

 of bony material used, there is a greatly increased 

 stability produced by the expansion of the lower 

 femur from a hollow shaft of compact bone to a 

 structure of much larger cross-section almost 

 entirely composed of spongy bone. 



"Significance of the Inner Architecture of the 

 Distal Part of the Femur. The function of the 

 lower end of the femur is to transmit through a 

 hinged joint the loads carried by the femur. For 

 stability the width of the bearing on which the 

 hinge action occurs should be relatively large. 

 For economy of material the expansion of the end 

 bearing should be as lightly constructed as is 

 consistent with proper strength. In accordance 

 with the principles of mechanics , 



FIG. 253. Epiphysial lines of femur in a young 

 adult. Anterior aspect. The lines of attachment of 

 the articular capsules are in blue. 



FIG. 254. Epiphysial lines of femur in a young adult. 

 Posterior aspect. The lines of attachment of the articular 

 capsules are in blue. 



