THE NERVOUS SYSTEM 309 



of two wrinkled hemispheres, situated opposite one another but united 

 at their base. The hemispheres are commonly confused with the brain 

 properly so called, but this name should be confined to that region 

 which contains the sensitive centre. 



The accessory organ which, when highly developed, confers mar- 

 vellous faculties on animals, rests upon the brain and covers it over 

 entirely, so as commonly to be confused with it ; for as a rule the name 

 of brain is given to the entire medullary mass enclosed in the cavity 

 of the cranium. We should however distinguish between the brain 

 properly so called and its accessory organ, however difficult the dis- 

 tinction may be ; for the accessory organ fulfils altogether special 

 functions, and is neither essential to the brain nor even to the 

 maintenance of life. It therefore deserves a special name, and I 

 propose to call it the hypocephalon. 



Now this hypocephalon is the special organ in which ideas and all 

 acts of intelUgence are carried out ; no such phenomena could take 

 place in the true brain, viz. that part of the main medullary mass 

 which contains the centre of communication of the nerves, and where 

 also the nerves of the special senses meet. 



If we regard the brain as that medullary mass which serves as the 

 meeting place for the various nerves, contains their centre of communi- 

 cation, and, in short, comprises the nucleus from which nervous fluid is 

 dispatched to the various parts of the body and to which it is returned 

 when it evokes any sensation, it will then be true to say that the brain 

 even of the most perfect animals is always very small. But when the 

 brain is provided with two hemispheres which cover it over and are 

 more or less confounded with it, and when these wrinkled hemispheres 

 become very large, it is customary to give the name of brain to the 

 whole medullary mass enclosed within the cranial cavity. Hence the 

 whole of this medullary mass is generally regarded as consisting of 

 only a single organ, whereas the fact is that it contains two, whose 

 functions are essentially distinct. 



Not only are the hemispheres special organs accessory to the brain, 

 but they are in no way essential to the existence of the brain ; this 

 is placed beyond doubt by many known facts, showing that lesions 

 may occur in them or that they may even be destroyed. With regard 

 to the functions fulfilled by the hemispheres, there must be an emission 

 of nervous fluid, which travels to these organs from its common reservoir 

 or nucleus and enables them to carry out the functions for which they 

 are adapted. Thus we may be sure that it is not the hemispheres 

 themselves which dispatch to the nervous system the special fluid 

 by which it works; for in that case the entire system would be 

 dependent on them ; which it is not. 



