39 



the active side of the head-ball, and increasing the 

 pressure exerted by it.^ 



The socket also moves forward. 



§ 40. It will be observed that the outward 

 movements, both of head-ball and socket, are in 

 opposition to the central forward movement of 

 the head-ball, and the force of each movement 

 being retained in the body by the setting of the 

 muscles, there will be a straining point between 

 the head-ball and socket, about the centre of the 

 joint. 



If the advance of the socket, which finally 

 reheves this strain, were made in anticipation of 

 the outward rotation of the socket, the joint would 

 not be freed until this rotation were accomplished. 



§ 41. These different positions of the head-baU 

 answering to those of the upper, now front points 

 of application, act in conjunction with a greater or 

 less number of subordinate front " points of appli- 

 cation" at the junction of the different S S formed 

 in the body of the snake. As mentioned in § 35, 

 these points are similar to the cross-Line points, 

 but, it seems to us, that it is only the section planes 



* This separation is caused by the posterior winding line, and this line 

 participates, throughout its course, in having its elements of pressure 

 reflected to the opposite side, as are those of the separating socket, in 

 fact, to the convex sides. 



