THE HUMAN SKELETON. 79 



admit of flexion and extension, and a certain degree of rota- 

 tion, while by their solidity and firm attachment to each 

 other, great strength is secured. 



29. We can now readily perceive how great the influence 

 of these twenty-four joinings must be in giving elasticity to 

 the whole column, and how much this must tend to the pro- 

 tection of the brain. Indeed, were it not for the interposi- 

 tion of this elastic material, every motion of the body would 

 produce a jar to the delicate texture of the brain, and we 

 should suffer almost as much in alighting on our feet, as in 

 falling on our head. 



30. But there is another very curious provision for the 

 protection of the brain, and that is the curved form of the 

 spine. By looking at the cut, you see that it is shaped like 

 an italic f. Now, suppose it were straight, and stood per- 

 pendicularly, it is evident that when we alighted on our feet 

 it would recoil with a sudden jerk, like a straight steel 

 spring pressed between the hands, from its extremities. In 

 such a case, the weight bearing equally, the spine would 

 neither yield to one side or the other, and consequently, there 

 would be a resistance, from the pressure on all sides being 

 balanced. |But shaped as it is, we find it constantly yielding 

 in the direction of its curves ; the pressure is of necessity 

 more on one side of the column than on the other, and its 

 elasticity is immediately in operation without a jerk. It 

 yields, recoils, and so forms the most perfect spring, admirably 

 calculated to carry the head without jar or injury of any 

 kind, 



3 jl When we reflect that the spinal column is composed 

 of so many separate parts, so nicely adapted to each other, 

 and kept in place by such a complicated array of ligaments, 

 tendons, and muscles, we might expect that injuries and dis- 

 eases of the structure would be very frequent. But fortu- 

 nately this is not the case, except where undue restraint and 

 confinement are imposed ; and it is only within a few years 



