xxii Obituary Notices of Fellows deceased. 



every case. Evolution not being entirely reversed, some level of evolution 

 is left. Hence the statement, ' to undergo dissolution,' is rigidly the equivalent 

 of the statement, 'to be reduced to a lower level of evolution.' In more 

 detail, loss of the least organised, most complex, and most voluntary, implies 

 the retention of the more organised, the less complex, and the more 

 automatic. This is not a mere truism, or, if it be, it is one that is often 

 neglected. Disease is said to ' cause ' the symptoms of insanity. I submit 

 that disease only produces negative mental symptoms answering to the 

 dissolution, and that all elaborate positive mental symptoms (illusions, 

 hallucinations, delusions, and extravagant conduct) are the outcome of 

 activity of nervous elements untouched by any pathological process ; that 

 they arise during activity on the lower level of evolution remaining" 

 (Croonian Lectures " On Evolution and Dissolution of the Nervous System," 

 1884, ' Brit. Med. Journ.,' 1, 1884). 



The three " levels " of evolution are thus described : — 



" I will state what I believe to be the hierarchy of nervous centres, which 

 accords with the doctrine of evolution. I used to arrange them according to 

 the morphological divisions of the nervous system — spinal cord, medulla 

 oblongata, etc. I now arrange them on an anatomico-physiological basis, 

 that is, especially as to degree of indirectness with which each represents the 

 body, or part of it. The lowest motor centres are the anterior horns of the 

 spinal cord, and also the homologous nuclei for motor cranial nerves higher 

 up ; they extend from the lowest spinal anterior horns up to the nuclei for 

 the ocular muscles. They are at once lowest cerebral and lowest cerebellar 

 centres ; hence lesion of them cuts off the parts they represent from the 

 whole central nervous system. I am ignoring the cerebellar system (see 

 infra, p. 6). The lowest centres are the most simple and the most 

 organised centres ; each represents some limited region of the body 

 indirectly, but yet most nearly directly ; they are representative. The 

 middle motor centres are the convolutions making up Ferrier's motor region. 

 These are more complex and less organised, and represent wider regions of 

 the body doubly indirectly ; they are re-representative. The highest motor 

 centres are convolutions in front of the so-called motor region. I say 

 1 so-called,' as I believe, and have urged for many years, that the whole 

 anterior part of the brain is motor, or chiefly motor. I speak more in detail 

 of this in another lecture. The highest motor centres are the most complex 

 and least organised centres, and represent widest regions (movements of all 

 parts of the body) triply indirectly ; they are re-re-representative. That the 

 middle motor centres represent over again what all the lowest motor centres 

 have represented, will be disputed by few. I go further, and say that the 

 highest motor centres (frontal lobes) represent over again, in more complex 

 combinations, what the middle motor centres represent. In recapitulation, 

 there is increasing complexity, or greater intricacy of representation, so 

 that ultimately the highest motor centres represent, or, in other words, 

 co-ordinate, movements of all parts of the body hi the most special and 



