132 EVOLUTION, OLD AND NEW. 



so also is the brain ; it is a soft and inelastic substance, 

 incapable therefore of producing or of propagating the 

 movement, vibrations, or concussions which result in 

 perception. The meninges, on the other hand, are 

 exceedingly sensitive, and are the envelopes of all the 

 nerves ; like the nerves, they take rise in the head ; and, 

 dividing themselves like the branches of the nerves, 

 they extend even to their smallest ramifications : they 

 are, so to speak, flattened nerves ; they are of the same 

 substance as the nerves, are nearly of the same degree of 

 elasticity, and form a necessary part of the system of 

 sensation. If, then, the seat of the sensations must be 

 placed in the head, let it be placed in the meninges, and 

 not in the medullary part of the brain, which is of an 

 entirely different substance. " * 



If this is so, it appears from what will follow as 

 though the meninges must be the " stock " rather than 

 the diaphragm. 



" What perhaps has given rise to the opinion that the 

 seat of all sensations and the centre of all sensibility is 

 in the brain, is the fact that the nerves, which are the 

 organs of perception, all attach themselves to the brain, 

 which has hence come to be regarded as the one 

 common centre which can receive all their vibrations 

 and impressions. This fact alone has sufficed to indi- 

 cate the brain as the origin of perceptions as the 

 essential organ of sensations ; in a word, as the common 

 sensorium. This supposition has appeared so simple 

 and natural that its physical impossibility has been 

 overlooked, an impossibility, however, which should be 

 * Tom. vii. p. 14, 1758 



