46 



change the leading points of apphcation, we are- 

 not able to say. 



Of the two articulating surfaces on the rib pro- 

 tuberance (§ 44), which constitute the ball portion 

 of the rib and spine-joint in the snake, we should 

 imagine that the rearmost one receives the press- 

 ure when the concavity of the rib faces forward, 

 the anterior one when it faces backward. 



§ 48. Returning to the action of the head-ball, 

 and of its socket (which latter is carried by the 

 first vertebra of the spine), we will endeavor to 

 carry out the principles stated, to a connection 

 with the ribs, &g., when concentrating the spring 

 for an act of progressive locomotion. 



(a) (§§ 39, 37). The head-ball rotates from the 

 left, by the rear, and toward the right, making 

 pressure in the left hemisphere of its socket, un- 

 der which a concave forms and its continued ac- 

 tion forms [against the passive resistance of the 

 right rear point of application, i. e., one of the 

 rear rib articulations on the right side], the "left 

 anterior winding line" (§ 25) in its secondary sec- 

 tion, i. e., in the posterior C of the S. 



{a') The continued rotation of the head-ball,, 

 against the passive resistance of the right rear 

 j)oint of application, after it has formed its second- 



