578 



THE NERVOUS SYSTEM 



employed a weak constant current in their experiments, applying a pair of 

 fine electrodes not more than one-twelfth inch apart to different parts of 

 the cerebral cortex. The results thus obtained have been confirmed and ex- 

 tended by Ferrier and many others, stimulating chiefly with induction currents. 



FIG. 407. 



FIG. 408. 



FIGS. 407 and 408. Brain of Dog, Viewed from Above and in Profile. F, Frontal fissure some- 

 times termed crucial sulcus, corresponding to the fissure of Rolando in man; S, fissure of Sylvius, 

 around which the four longitudinal convolutions are concentrically arranged; i, flexion of head 

 on the neck, in the median line; 2, flexion of head on the neck, with rotation toward the side of the 

 stimulus; 3, 4, flexion and extension of anterior limb; 5, 6, flexion and extension of posterior 

 limb; 7, 8, 9, contraction of orbicularis oculi and the facial muscles in general. The unshaded part 

 is that exposed by opening the skull. (Dalton.) 



The fundamental phenomena observed in all these cases may be thus 

 epitomized : 



i. Excitation of the same spot on the cortex is always followed by the same 

 movement in the same animal. 2. The area of excitability for any given 



