UPON THE SERIES OF PREHISTORIC CRANIA. 673 



logical variability of these convolutions, it does justify us in 

 ascribing to them a lesser physiological activity. 



Leaving now the consideration of the distribution of arteries 

 over this particular area of the cerebral cortex as detectible by the 

 naked eye, we come to a consideration of the histological characters 

 of this zone as compared with that of the fronto-parietal convolutions 

 which lie anteriorly to it. And it is a fact of cardinal importance 

 that it is in this anteriorly situated part of the brain that the large 

 pyramidal cells, the ' cornu ammonis formation ' of Meynert, so 

 characteristic of the healthy human brain, are chiefly, if not 

 exclusively, found. The largest indeed of these pyramidal cells, 

 ' Riesenpyramiden,' have been said by Professor Betz to be limited 

 in their distribution posteriorly by the line of the fissure of 

 Rolando (see Centralblatt. Med. Wiss. 1874), and Dr. Achille 

 Foville (Medical Examiner, Feb. 1, 1877, p. 85) does but extend 

 the area in which they are all but exclusively to be found, just 

 so much further back as is the second ascending central convolu- 

 tion which forms the posterior boundary of that fissure. Dr. Major 

 (Journal of Mental Science, Jan. 1876) has justly insisted upon the 

 indications with which human pathology firstly, as shown by him 

 in the West Biding Asylum Reports, 1872, vol. ii. pp. 41-52, and 

 comparative anatomy secondly, furnish us as to the functional 

 importance of these pyramidal cells ; it being in these cells that 

 ' degenerative changes first occur when age is beginning to do its 

 work and pari passu the intellect is failing,' whilst 'as we proceed 

 downwards in the scale of development it is these cells which vary 

 most distinctly from the corresponding bodies in the human organ.' 

 To this I would add that the histological characters of these cells 

 when compared with those of other cells known to discharge 

 important functions with great activity are such as to vindicate 

 their claim to a high rank amongst such cells. As seen in a 

 microscopic specimen prepared by the ordinary reagents, these cells 

 are remarkable, firstly, for their large size ; then for their freedom 

 from the limitation of a cell wall ; thirdly for the clear lacunar spaces 

 in which they lie ; fourthly, for their angular nucleolated nucleus 

 prolonged at its angles into processes somewhat like those of the 

 cell itself; fifthly, for these processes themselves, apical, basal, and 

 lateral. Those who are impressed with the value of the hypothesis 

 put forward by the late Professor Parkes l to the effect that in a 



1 Proceedings of the Royal Society, June 20, 1867, xvi. 94. Dr. Parkes having 

 discovered that though active exercise produced no immediate increase in the eliinina- 



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