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XIII. — On the Minute Structure of the Brain in the Chipanzee, and of the 

 human Idiot, compared with that of the perfect Brain of Man ; with some 

 Reflections on the Cerebral Functions. By James Macartney, M. D., 

 F. R. S., F. L. S., M. R. I. A., &c. &c. 



Read June 27, 1842. 



JVIANY years ago I discovered, with only a common pocket lens, a reticulation 

 of fine white fibres, immediately under the surface of the cerebrum, in birds. 

 This first led me to believe that the medullary fibres, as they are called, extended 

 farther, and were more subdivided than had been hitherto supposed. I have since 

 been able to demonstrate to medical students, and to several teachers of anatomy, 

 the existence of those filaments in every part of the brain, by simply moistening 

 the substance of the organ, during the dissection, with a solution of alum in 

 water, which has the effect of slightly coagulating, and rendering the finer fila- 

 ments visible, which, in their natural condition, are transparent. By this means, 

 I have shown that the filaments (which I prefer to call sentient, instead of white 

 or medullary) everywhere assumed a plexiform arrangement, and that the most 

 delicate and intricate plexusus were to be found inclosed in the grey or coloured 

 substances of the brain. This fact proves the analogy between the coloured sub- 

 stances of the brain, and the ganglia of the nervous system, in which there is a 

 close reticulation of nervous fibres. I have long been in the habit of consider- 

 ing the magnitude and form of the entire brain, and of its several parts, as being 

 merely subservient to the number, extent, and connexions of the various plexuses, 

 in which, and especially in those occupying the coloured substances, I believe the 

 sensorial powers of the brain to reside. 



A Chimpanzee (the pigmy of Tyson) having some months ago died in Dub- 

 lin, and the dissection of it having been entrusted to Mr. Wilde, I proposed to 

 him that I should undertake the examination of the animal's brain, in my own 



