38 



will give to the socket a forward moyement with a 

 turn to the right, but when constrained by the 

 action of the other winding line directly forward, 

 a' and h' combined tend to liberate the head-joint, 

 but, as will be noticed further on, the locomotive 

 gathering requires that a considerable part of h' 

 precede h. 



§ 38. The outward motion of the right side of 

 the socket, if transformed into motion of the left 

 side of the head-ball, would double it, and the 

 ■same for the motion of the head-ball in relation to 

 the socket motion. 



§ 39. We think, then, that we may, for our 

 purposes, describe the movements, actual and rela- 

 tive, in the head-joint, as follows, for the left-right 

 opposition of forces. 



{a) The head-hall performs a rotary movement 

 to the left and backward, pressing downward on 

 the left lateral heniisphere of the socket. This 

 pressure passes forward. 



{h) The right-haK hemisphere of the socket 

 performs a rotary movement to the right and 

 backward, at the same time drawing itself away 

 from the corresponding part of the head-ball, and 

 consequently raising the left side of the socket under 



