Dr. Macartney on the Structure of the Brain in the Chimpanzee, ^c. 323 



manner. Tyson and others had described the bulk, shape, and external appear- 

 ance of the different parts of this creature's brain, but the intimate structure had 

 never been examined by any anatomist. 



I shall now lay before the Academy an account of what I observed in the 

 brain of the Chimpanzee, and likewise in those of two idiots ; by which it will 

 appear that the brain in the latter possesses a still lower degree of organization, 

 than in the former animal. 



DISSECTION OF THE BRAIN IN THE CHIMPANZEE (siMIA TROGLODYTES. LIN.) 



The external for^n bore so great a resemblance to the human brain, that, 

 excepting the difference in size, the one might be mistaken for the other. The 

 convolutions were as decidedly marked, and the proportions of the cerebellum to 

 the cerebrum were exactly as in man. On the under surface of the brain I ob- 

 served that the two white pea-shaped bodies, called corpora candicantia, were 

 very indistinct ; and they did not appear to be, as in man, the continuation of the 

 anterior crura of \he fornix. The pons, which unites the lateral lobes of the 

 cerebellum, was, perhaps, rather flatter than in the human subject, and the fifth 

 pair of nerves entered it, and passed for a little way distinctly, which is so re- 

 markable in the sheep. The pyramids did not decussate to any extent ; only 

 two superficial bundles of fibres crossed. The corpora olivaria did not project 

 distinctly, and the band which surrounds them was not observed. The structure 

 internally of these bodies consisted of white filaments included in grey substance. 

 The branches of the arbor vitce were, perhaps, not so deep, but quite as numerous 

 as in us. The white filaments composing the trunk were not so fine, nor so 

 strictly interwoven, as in man, and therefore they were more easily distinguished. 

 The corpus Jimbriatutn was a long shape, and appeared to be composed chiefly 

 of grey substance, and wanted the denticulated edge. The part called locus 

 niger, in the crura of the cerebrum, was a small, greenish-grey mass, of an irre- 

 gular figure, and less than a pea, instead of the crescentic form, as in man ; and 

 it did not mingle with the white fibres of the crus. The pineal gland was large. 

 It was removed in making a cast of the ventricles, and lost ; it was not, therefore, 

 ascertained whether it had any calcareous matter in it or not. The parts in the 

 lateral ventricles corresponded very nearly with the same in man. The soji com- 



2t2 



