136 



§ 131. Although the ophidian, composite, and 

 bi-composite spines begin the development of the 

 winding lines, separately, yet, once begun, each 

 continues its development throughout ; that is, 

 until the anterior winding line, beginning in the 

 ophidian S, has formed its bi-composite portion, 

 the ophidian action constantly increases along 

 with the others, and so also for the posterior wind- 

 ing line. Thus, the final action still centres be- 

 tween the upper and lower lung lobes (§ 99). 



§ 132. It wiU be remembered (§§ 32, 33, 34) that 

 to bring both C C of any S into a discharge for- 

 ward, the cross-line must be displaced, and the pos- 

 terior C rests, for its point of reaction, against the 

 plane in which the anterior point of apphcation 

 moves. For this reason the ophidian posterior C 

 thus rests against the neck-root plane ; the poster- 

 ior C of the rear half of the composite spine (its 

 junction with the central S being formed) rests 

 against the same point. The final point of reaction 

 will be at the base of head, to which the points of 

 all the spines will be transferred. 



These posterior C C, their appuis (the hind-leg, 

 &c.) being fixed, thrust their points of reaction for- 

 ward, and (though the anterior C C discharge, so 



