60 
ON MECHANICAL ARRANGEMENT 
The structure of the spine is not in general different in 
different animals. In the serpent tribe, however, it is con¬ 
ed, the membranes recoil by their elasticity, the gristle is pressed into its 
place, and the bones resume their position. 
We can readily understand 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 protection of the brain. Were it not for this 
interposition of elastic material, every motion of the body would produce 
ajar 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. It is, as we have 
already remarked, necessary to interpose thin plates of lead or slate be¬ 
tween the different pieces of a column to prevent the edges (technically 
called arrises) of the cylinders from coming iu contact, as they would, in 
that case, chip or split off. 
But there is another very curious provision for the protection of the 
brain; we mean the curved form of the spine. If a steel spring, perfectly 
straight, be pressed between the hands from its extremities, it will resist, 
notwithstanding its elasticity, and when it does give way, it will be with 
a jerk. 
Such would be the effect on the spine if it stood upright, one bone 
perpendicular to another; for then the weight would bear equally; the 
spine would yield neither to one side nor to the other; and, consequently, 
there would be a resistance from the pressure on all sides being balanced. 
We, therefore, see the great advantage resulting from the human spine 
being in the form of an italic f. It is prepared to yield in the direction 
of its curves; the pressure is of necessity more upon one side of the col¬ 
umn 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. 
The most unhappy illustration of all this is the condition of old age. 
The tables of the skull are then consolidated, and the spine is rigid: if an 
old man should full with his head upon the carpet, the blow, which would 
be of no consequence to the elastic frame of a child, may to him prove 
fatal; and the rigidity of the spine makes every step which he takes, vi¬ 
brate to the interior of the head, and jar on the brain. 
We have hinted at a comparison between the attachment of the spine 
to the pelvis and the insertion of the mast of a ship into the hull. The 
mast goes directly through the decks without touching them, and the heel 
of the mast goes into the step, which is formed of large solid pieces of 
oak timber laid across the keelson. The keelson is an inner keel resting 
upon the floor-timbers of the ship and directly over the proper keel. 
These are contrivances for enlarging the base on which the mast rests 
as a column; for as, in proportion to the height and weight of a column, 
its base must be enlarged, or it would sink into the earth; so, if the mast 
were to bear upon a point, it would break through the bottom of the 
ship. 
The mast is supported upright by the shrouds and stays. The shrouds 
secure it against the lateral or rolling motion, and the stays and backstays 
against the pitching of the ship. These form what is termed the standing 
rigging. 
The mast does not bear upon the deck or on the beams of the ship; in¬ 
deed there is a space covered with canvass between the deck and the 
mast. 
