212 Leyton and Sherrington 



other regions yielded responses in which no abnormality was detected on 

 the left side any more than on the right. The bulb and cord were 

 subsequently sectioned and examined by the Marchi method for degenerat- 

 ing tracts as far forward as the vipper half of the pons. The pyramidal 

 tracts showed no degeneration, either in pons, bulb, or cord. 



A third experiment, similar to the preceding, but with a lesion extend- 

 ing farther down the centralis posterior, resulted similarlj^, no obvious 

 effects being detected. We tried the lower part of the gyrus by preference, 

 because it is in that part that previous experimenters placed extensive 

 motor centres. 



V. The Insula. 



In one chimpanzee we exposed the insula for the larger portion of its 

 extent, and tested its surface by faradism, both by the unipolar and the 

 bipolar method. To expose it, the lower portion of gyrus centralis anterior, 

 which had been examined by stimulation and given the usual results, had to 

 be removed. From the whole surface of insula tested we obtained no detect- 

 able results, although the gyrus centralis anterior where not removed con- 

 tinued at the time to respond readily. Two fissures exposed in the insula 

 were also opened up and the electrode applied, but no result was elicited. 



VI. The Thresholds of Faradic Excitability of the Motor Cortex 

 OF Cat, Macaque Monkey, and Chimpanzee compared. 



We made some observations in regard to this by a procedure for 

 the suggestion of the electrical arrangement of which we are indebted 

 to Professor J. S. Macdonald. Cat, macaque (Macacus sinicus), and 

 chimpanzee were anaesthetised by chloroform and ether mixture in the 

 usual way. In each animal the motor cortex was then exposed suitably 

 for stimulation of the fore-limb area. A copper plate with binding screw 

 was applied over a pad of cotton-wool soaked in strong salt solution to the 

 shaved skin of the hind-leg in each animal (fig. 29). The copper plate 

 applied to one of the animals (A) was attached by a wire to one end of the 

 short-circuiting key in the secondary circuit of the physiological induc- 

 torium. Another wire attached the binding screw on the handle of an 

 electrode of the pattern (stigmatic) used by us for unipolar faradisation to 

 the copper plate on a second of the animals (B), and to the copper plate 

 attached to the third animal (C) a similar electrode was similarly attached. 

 Finally, to the short-circuiting key on its side opposite that connected with 

 the copper plate on animal (A) a wire attached a third electrode of similar 

 pattern to the other two, The secondary circuit's short-circuit key being 

 closed, three persons in separate charge of the three animals, and each 

 controlling one of the stigmatic electrodes, applied his electrode to a spot 

 in the "arm area" of cortex, the spot being in each case one which had 

 been found to elicit flexion of elbow. The three animals were thus 

 connected in series in the secondary circuit of the inductorium beyond the 



