644 Sir James Crichtoii- Browne [May 3, 



I shall pass rapidly before you photographs of the braius of a few 

 of the primates, showing progressive convolutional elaboration. 



In the Ouistiti, Jacchus vulgaris, or Marmoset monkey, an 

 attractive but weak-minded member of the monkey tribe, the hemi- 

 spheres are almost as smooth as in the rabbit, and show just two 

 rudimentary sulci or folds (Fig. 19). 



In the Pincho monkey, or Midas oedijjus, a South American 

 species, in intelligence about the Marmoset level, we have deepening 

 of these folds and the appearance of two new ones (Fig. 20). 



In the Moloch monkey, the Callithrix Moloch, a stage higher in 

 intelligence, we have these folds repeated and extended and supple- 

 mented by others of a very distinctive character (Fig. 21). 



In the Sapajou, another South American monkey (Fig. 22), we have 

 still further convolutional complexity, and I would ask you particularly 

 to note that in these lower forms — in this one, the Sapajou, and in this, 

 the Mangabey — Cercopithecus JEthiops (Fig. 23), an African species, 

 there is almost perfect symmetry in the two hemispheres as regards 

 their foldings, a symmetry w^hich becomes less and less marked as 

 we ascend the scale. 



There is still a good deal of symmetry in the hemispheres of the 

 Chimpanzee brain (Fig. 24), though less than in the Mangabeys, and 

 as regards convolutional complexity you w^ill have no difficulty in 

 perceiving that that is really much more intricate and advanced in 

 the Chimpanzee than in the brain of the human microcephalic idiot, 

 a representation of which is next thrown on the screen (Fig. 25), 

 and in that idiot brain you will notice another striking feature in 

 which it resembles that of the Chimpanzee, and that is the exposure 

 of the cerebellum when the brain is looked at from above. 



Nothing of that kind is seen in even a low type of the normal 

 human brain like that of the Hottentot (Fig. 26), in which pray 

 observe that the convolutions are larger and more regular and sym- 

 metrical than in the brain of au European which I next show you 

 (Fig. 27). This is an average European human brain, not that of a 

 highly intellectual person, in which the convolutions would be smaller 

 and more numerous, but it illustrates clearly the multiplication of 

 ridges and hollows in the brain of the civilised human being and the 

 divergence in the form, twistings and arrangements of the convolu- 

 tions in the two hemispheres. Rigid symmetry has disappeared and 

 we have reached a condition of right and left-brainedness. 



But throughout this symmetry and variability in the ])rain — and 

 no two human brains were ever exactly alike in their convolutional 

 arrangement — we can invariably recognise one plan of construction 

 and identify all the main convolutions, however they may contort 

 themselves and put forth secondary gyri. And more than that, we 

 can now, thanks to the brilliant discoveries of Fritch and Hitzig, 

 Ferrier, Victor Horsley, Sherington and others, assign specific 

 functions to certain of the convolutions. We know that there are 



