OF THE UNDERSTANDING 367 



and the impressions graven upon it. This organ, together with the 

 brain and nerves, differs from all the other organs of the animal body- 

 in that it is not active, and does no more than provide the means for the 

 nervous fluid to carry out its various phenomena. 



Indeed, when I remember the extreme softness of the medullary- 

 pulp constituting the nerves, brain, and hypocephalon, I cannot think 

 that in the relations of the nervous fluid with the medullary parts, 

 the latter are capable of exerting the slightest action. Beyond doubt 

 these parts are entirely passive and unable to react upon anything that 

 affects them. Hence it results that the medullary parts, of which 

 the hypocephalon consists, receive and preserve the traces of all the 

 impressions made upon them by the movements of the nervous fluid ; 

 so that the only active element in the functions of the hypocephalon 

 is the nervous fluid itself; or to express the matter more precisely, 

 the organ carries out no function, the nervous fluid by itself carries 

 out all ; but this fluid could in nowise give rise to them without the 

 existence of the organ in question. 



I may be asked how it is possible to conceive that any fluid, however 

 subtle and varied its movements, can by itself give rise to that astonish- 

 ing variety of acts and phenomena characteristic of the intellectual 

 faculties. To this I reply, that the entire marvel is in the composition 

 of the hypocephalon itself. 



The medullary mass constituting the hypocephalon, that is, the two 

 wrinkled hemispheres which cover over the brain, — this mass, I say, 

 which seems to be only a pulp, whose parts are continuous and coherent 

 throughout, consists, on the contrary, of an inconceivable number of 

 separate and distinct parts, from which result a vast quantity of 

 cavities of infinitely varied size and shape and appearing to occupy 

 distinct regions, equal in number to the intellectual faculties of the 

 individual ; lastly, however it may come about, the composition 

 of the organ is different in each region, for each is devoted to some 

 individual faculty of the intelligence. 



The examination of the white medullary part of the hypocephalon 

 has disclosed numerous fibres in it : now it is probable that these fibres 

 are not, as elsewhere, organs of movement ; their consistency would not 

 permit of it : there is more reason to believe that they are so many 

 individual canals, each terminating in a cavity which would be in the 

 form of a cul-de-sac unless they communicate together by lateral paths. 

 These cavities, which are imperceptible to us, are as innumerable as the 

 tubular threads leading to them ; and it may be presumed that it is 

 on their internal walls that the impressions brought by the nervous 

 fluid are engraved ; there may also be little medullary plates or leaves 

 for the same purpose. 



