The Excitable Cortex of the Chimpanzee, Orang-Utan, and Gorilla 221 



17. Ablations of portions of the free surface of gyrus centralis posterior 

 fjdve rise to no obvious symptoms of paresis, nor, in the one case whose bulb 

 and spinal cord were examined, to detjeneration of the pyramidal tract. 



18. The threshold of faradic excitability of the motor cortex, as tested 

 in the arm area, seems to be practically similar in cat, macaque, and 

 cliimpanzee. 



19. In some chimpanzees occlusion of the two carotid arteries renders 

 the motor cortex inexcitable to faradism, and does so rapidly, e.g. 2 minutes. 

 After release of the arteries, responses to faradic stimulation reappear in 

 about H minutes. In one animal occlusion of one carotid alone reduced 

 the excitability of the motor area of the corresponding hemisphere almost 

 to extinction, but in another animal occlusion of one carotid alone did 

 not markedly depress the excitability. The anthropoid brain, unlike the 

 brain of the smaller monkeys, has frequently a Circle of Willis of human 

 pattern (20). 



20. In a chimpanzee with a cranial vault of about the thickness of the 

 average human, the application of local cold (ice-bag) and warmth over the 

 parietal scalp rapidly atiected the temperature of a thermometer bulb lying 

 under the dura against the cerebral surface beneath the region of applica- 

 tion of the local cold or warmth outside. 



It is a pleasure to express here our thanks to Professor Harvej'^ 

 Cushing of Boston, to Dr A. W. Campbell of Sydney, and to Dr Alfred 

 Frolilich of Vienna for valued co-operation and kind assistance in many 

 of the experiments. To Dr Besredka, Dr Weinberg, and the late 

 Professor Metchnikoff of the Institut Pasteur we are indebted for one 

 of the orangs used. We have much pleasure too in recording our acknow- 

 ledgment of the energy of Mr E. G. Cox, assistant in the laboratory, in 

 obtaining the animal material, and of his skill and care in all matters 

 pertaining to the management of it. 



LIST OF REFERENCES. 



(1) Bayliss, W. M., Principles of General Physiology, London, 1915, 480. 



(2) Beevor, C. E., and V. H. Horsley, Phil. Trans., B, 1890, 129. 



(3) Graham Bkowx, T., this Journal, 1915, ix. 81 ; ibid., 101 ; ibid., 117; 

 ibid., 131. 



(i) Graham Brown, T., Proc. Physiol. Soc, pp. xxix, xxx, xxxiii, in Journ. 

 Physiol., 1914:, vol. xlviii. 



(5) Graham Brown, T., and C. S. Sherrington. Proc. Roy. Soc, 1912, B, 

 Ixxxv. 250. 



(6) Graham Brown, T.. and C S. Sherrington, Proc. Physiol. Soc, 1913, 

 p. xxii, in Journ. Physiol., vol. xlvi. ; Brit. Med. Journ., 1913, ii. 751. 



(7) Graham Brown, T., and C. S. Sherrington, Journ. Physiol., 1911, xliii. 209. 



