REGARDED AS \ MASS. 
121 
ble a membrane as the periosteum invested the teeth, as it 
invests every other bone of the body, their action, necessa¬ 
ry exposure, and irritation, would have subjected the ani¬ 
mal to continual pain. General as it is, it was not the sort, 
of integument which suited the teeth. What they stood in 
need of, was a strong, hard, insensible, defensive coat; and 
exactly such a covering is given to them, in the ivory 
enamel which adheres to their surface. 
2. The scarf-skin, which clothes all the rest of the body, 
gives way, at the extremities of the toes and fingers, to nails. 
A man has only to look at his hand, to observe with what 
nicety and precision, that covering, which extends over 
every other part, is here superseded by a different sub¬ 
stance, and a different texture. Now, if either the rule 
had been necessary, or the deviation from it accidental, 
this effect would not be seen. When I speak of the rule 
being necessary, I mean the formation of the skin upon the 
surface being produced by a set of causes constituted with¬ 
out design, and acting, as all ignorant causes must act, by 
a general operation. Were this the case, no account could 
be given of the operation being suspended at the fingers’ 
ends, or on the back part of the fingers, and not on the 
fore part. On the other hand, if the deviation were acci¬ 
dental, an error, an anomalism; were it anything else than 
settled by intention; we should meet with nails upon other 
parts of the body. They would be scattered over the sur 
face, like warts or pimples. 
3. All the great cavities of the body are enclosed by 
membranes, except the skull. Why should not the brain be 
content with the same covering as that which serves for the 
other principal organs of the body? The heart, the lungs, 
the liver, the stomach, the bowels, have all soft integuments, 
and nothing else. The muscular coats are all soft and 
membranous. I can see a reason for this distinction in the 
final cause, but in no other. The importance of the brain 
to life, (which experience proves to be immediate,) and the 
extreme tenderness of its substance, make a solid case 
more necessary for it, than for any other part; and such a 
case the hardness of the skull supplies. When the small¬ 
est portion of this natural casket is lost, how carefully, yet 
how imperfectly is it replaced by a plate of metal? If an 
anatomist should say, that this bony protection is not con¬ 
fined to the brain, but is extended along the course of the 
spine, I answer, that he adds strength to the argument. If 
he remark, that the chest also is fortified by bones, I reply, 
that I should have alleged this instance myself, if the ribs 
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