ANATOMY 



hard, condensed bone, thickest towards the middle 

 of the shaft and gradually thinning or tapering 

 off towards either extremity. The large expanded 

 extremities are seen to be covered by a tenuous 

 shell of condensed bone of almost egg-shell thin- 

 ness, and are not occupied by a cavity, but filled 

 by an open-work or honeycomb arrangement of 

 bony substance usually termed * spongy bone, 5 but 

 for which the term c lattice-work ' is preferable. 



The shaft or columnar part of the thigh-bone 

 is especially liable to what, for the sake of sim- 

 plicity, may be termed breaking forces, and a 

 simple experiment will furnish a convincing proof 

 that a tube or hollow cylinder is a most efficient 

 construction for resisting such forces. 



If a stick about half an inch in diameter is 

 slowly broken by holding it in the two hands and 

 pulling either end towards the holder, it will be 

 noticed that on the far side the substance of the 

 stick is rended or pulled apart, while on the near 

 side it is forced together or crushed. Further, 

 it will be obvious that at the beginning of the 

 breaking it is the parts of the stick towards the 

 surface which first give way, torn apart on the far 

 side and crushed on the near, while the more 

 deeply situated substance of the stick towards its 

 centre must feel the breaking force to a less extent, 

 and is in a situation where it cannot play such an 

 efficient part in resisting the strain. From this it 



21 I 



