150 



line end as it draws that end of the alternate 

 cross line toward the right, and releasing also the 

 original posterior cross-line end from its con- 

 strained position to the left, that this virtual dis- 

 charge is carried out and the alternate false rib 

 propellers are grounded. 



The analogy of the snake's action holding good 

 for the three spines and their appuis, the right 

 hind-foot will be set down when A' a'^ has re- 

 leased the cross-line end of the comj^osite spine 

 at the jimctnre of the lumbar and ophidian ver- 

 tebrae. 



As has been so fi'equently said (§ 39, etc.), all 

 the actions of the posterior lines are " replace- 

 ment" movements in the side of the C which they 

 affect. Thus the inward rolling of the left digas- 

 tric is really consequent on an inoperative outward 

 rolling of the right digastric, in the same way as 

 the pressure of the left head socket comes from 

 the drawing away of the right one. 



b^ Posterior right winding-line. Effects in ^^os- 

 terior C of the re-action from its secondary section 

 as checked in anterior C, brings the left propel- 

 ler false ribs on to their inner beariags, beginning 

 at the rear, and produces an effect in the further 

 stretching of the left side of the diaphragm by 



