OF THE SPINE. 227 



which would be the consequence of the surfaces 

 being horizontal. If a cannon were made to re- 

 coil upon an ascending plane, or a surface form- 

 ing a portion of a circle, it would represent the 

 mechanism of the articulating processes of the 

 vertebrae. 



Let the separate spine be presented before us, 

 it stands up, like a mast, broad and strong below, 

 and tapering upwards. The mast of a ship is 

 supported by the shrouds and stays ; and if we 

 sought for an analogy with these, we must fix 

 upon the long muscles of the back, which run 

 along the spine to sustain it. But as a mast goes 

 by the board in a storm, we see where the spine 

 would have been most in danger, had not nature 

 provided against it. When we start forward in 

 walking or running, it is by the exertion of the 

 muscles of the lower extremities, and the body 

 follows. Did the spine stand directly up perpen- 

 dicularly, it would sustain a shock or jar at its 

 base in these sudden motions. We see, there- 

 fore, the intention of the lower vertebrae being 

 inclined forwards from their foundation on the 

 sacrum : for by this means, the jar which might 

 endanger the junction of the lowest piece, is di- 

 vided amongst the five pieces that form the curve. 

 The same thing is seen in the quadruped : for as 

 the spine in the back and loins lies horizontally, 

 and the neck rises towards the perpendicular, 

 there would be danger of dislocation, if the ver- 

 tebrae of the neck rose suddenly and abruptly 



