91 



bone, which (§ 87) must place the intermediate 

 points of traction in position before the head and 

 pelvis act upon each other. This makes necessary 

 an extra spiral-line movement, very much more 

 extended than any for the connection of the S S, 

 or C C, in the snake's contortions, and wliich can- 

 not be accommodated on one surface. It takes 

 place, for the transition from the anterior ivinding- 

 line of the " ophidian " to that of the " composite- 

 spine'' at the posterior end of eitJier condyle ; and 

 for the similar movement hetiveen the posterior lines 

 at the anterior end. 



Further, when the neck, S, allows this eccentric 

 movement to the upper part of the chest, the line 

 of pressure becomes oblique, and to resist this the 

 condyle-sides must be rounded in the perpendic- 

 ular plane. For example, the inner side of the 

 left condyle to meet the movement of the upper 

 part of the chest to the left, which accompanies 

 the establishment of the primary section of the 

 left anterior line, and its exterior side against the 

 movement to the right, which accompanies the 

 formation of the secondary section of the right 

 posterior line, exerted against this side by the up- 

 ward movement of the socket reciprocal to its 

 withdrawal on the right §67 (h). 



