120 



the three spines* — ophidian, composite and bicom- 

 posite {§ 84) — it will be observed, at the head 

 ball and socket joint, that the result of a ball and 

 a socket action, fuUy carried out, is to, as it were, 

 throw off the point of pressure and the pair of coun- 

 ter-acting lines on which it depends to the front, dis- 

 engaging them, one from the other, each to its own 

 side. And if, as in the curve of " superimposition " 

 (§ 71), there be two pairs of counter-acting lines, 

 both are thus thrown forward and disengaged lat- 

 terally. In either case, if not discharged, they 

 will straighten, and, in the case of one pair, this 

 position protracted will bring the other pair into 

 action, and, suppressing the lateral developments, 

 will produce double superimposition (§ 71), and 

 make the tractions collateral instead of, as before, 

 diagonal (§ 71). 



Now, before the whole course of the lines for aU 

 the spines are thus made collateral, this baU and 

 socket action occurs at four points : 



First. — Between the upper and lower lung lobes, 

 for the ophidian S. 



Second. — At the diaphragm, for the union between 

 the central and third S. 



* When considering the bony spine only in relation to its S S S, we 

 have called them First, Central and Third. 



