NATURAL THEOLOGY. 27 



in this wonderful piece of mechanism, to fit it for the 

 purposes it has to answer. 



T. There is, at least one happy circumstance 

 more, deserving to be mentioned, and that is one 

 which contributes to the safety of the brain, even 

 when the head is broken in. Can you describe it ? 



A. The principal lining of the head, which anato- 

 mists call the dura mater, (dura, — hard and unyield- 

 ing, to signify its strength), is so substantial a mem- 

 brane, that when the skull is fractured, it is not easy 

 for the pieces to fall in. In this respect, it may be 

 compared to the skin upon the outside of an egg, 

 which we often see preserving the form of the egg en- 

 tire, when the shell is broken in a thousand pieces. 

 But for this, the surgeon would rarely be able to raise 

 the fragments of a skull without fatal consequences to 

 the brain. This lining is found also in the spine, 

 which contains a continuation of the substance of the 

 brain. We discover no such lining in the hollows of 

 the other bones. They contain nothing which re- 

 quires it. 



T. You spoke of the packing of the brain as re- 

 markable. There is another instance, more curious 

 still, of the same kind. 



A. There is a place where the membranes that 

 enclose the brain suddenly turn inward, and divide it 

 into two parts, so as to prevent one part from pressing 

 upon the other. The partition takes place in a re- 

 markable situation. It is where that portion of the 

 brain called the cerebrum, and which occupies the for- 

 ward and upper part of the head, begins to descend 



