330. 



ANIMAL MECHANICS. 



is the shortest line between the directions, and perpendicular 

 to both. Draw I'X parallel to IA, and let 



IT = 2C 



A'I'X= 2 f 



Take C, the centre of the line //', and draw Cx parallel 

 to the bisector o£XI'A\ and draw Cy perpendicular to Cx 



Fig. 89. 



and to IP ; and take CI for the axis of 2. Let Cx, Cy, Cz 

 be the axes of co-ordinates, then the equations of the bones 

 AB and AB' will be 



y - mx = 0 z — c = o 



y + mx = 0 z + c = o. (80) 



where m = tan 0. 



Hence, the equations of any two planes passing through 

 AB erndA'B', respectively, will be 



(y - mx) + A {z - c) = o 



{y + mx) + X' (z + c) = o, (81) 

 where A, A' are arbitrary parameters. 



