ANIMAL MECHANICS. 



263 



cular to the bisector of the muscular fibres, when lying in the 

 same plane, and investigate the relations between the bones 

 which are necessary to produce a maximum effect, when the 

 muscle contracts. 



In Fig. 69, AB and A'B' are the two bones, A'B being 

 supposed fixed, and AB moveable, round an axis SK, pass- 

 ing through the fixed socket S, and perpendicular to OX 



Fig. 69. 



the bisector of the muscular fibres. Let ad be any fibre 

 which takes the position db, when a small rotation occurs 

 round the axis SK, moving the point a to b, which lies out- 

 side the plane ABA'B'. 

 In the triangle adS, let 



ad - aO — a' 0 - I - l = p 



aS - A a'S = A' aSd = x. 



