118 OF THE DISEASES 



side, because the crust is thinner on the inside than 

 on the outside. 



Two advantages are gained by the diminution of 

 the thickness of the crust on the inside : first, the 

 chance of the interference of one foot with the 

 other leg is lessened ; and secondly, greater 

 elasticity is afforded. More elasticity is required 

 on the inside than on the outside, in order to 

 obviate the greater concussion which, as is well 

 known, falls on the inside. 



Greater concussion falls on the inside, because 

 greater weight falls on it than on the outside. 

 It may seem strange to the reader that less thick- 

 ness of crust should be given to that side on which 

 the greater weight falls. But a similar formation 

 with a similar view, viz. elasticity and the lessening 

 thereby of concussion, is found throughout on the 

 inside of the limb up to the knee. 



In considering, however, the strength required 

 on the inside, it is important to bear in mind three 

 points : first, although the greater weight falls 

 towards the inside, yet it falls on it more perpen- 

 dicularly than it does on the outside, and the two 

 inside crusts or props are therefore more directly 

 under the centre of gravity than the two outside 

 crusts ; secondly, the two inside are nearer together 

 than the two outside crusts, and therefore each 

 requires less strength — a principle well known to 

 all builders ; thirdly, the fibres of the crust on the 



