BONE-BUILDERS 



77 



the most perfect of all levers which man has invented 

 for the lifting of heavy weights. Every beam of bone in 

 the neck of the femur, he said, had been given the shape, 

 thickness, and position which ensured the greatest strength 

 with the greatest economy of material. Everywhere in 

 the body we find the same perfect design in the work of 

 bone-builders. 



What is still more wonderful, is the fact that these 



Fig. 21. — The construction of the upper end of the thigh-bone, as depicted by 

 Professor F. Dixon, compared with a drawing of Fairbairn's crane (W. Finerty). 



elaborate bony constructions are being constantly altered 

 and rebuilt during the twenty years of growth. That can 

 best be understood by looking at fig. 22. The upper part 

 of a thigh-bone in the fifth year of growth is represented 

 (A) ; when growth has proceeded to the fifteenth year the 

 head and neck will have reached the position shown on 

 the figure. Now, if growth were merely a stretching of 

 the shaft, the architecture of the neck would merely be 

 pushed up and enlarged to match the increase in the size 



