FUNCTIONS OF THE BRAIN. 31 



Spheres were not locally separated, but carried on eacli by 

 the aid of the whole organ. Hitzig in 1870 showed, how- 

 ever, that in a dog's brain highly specialized movements 

 could be produced by electric irritation of determinate 

 regions of the cortex ; and Ferrier and Munk, half a dozen 

 years later, seemed to prove, either by irritations or excis- 

 ions or both, that there were equally determinate regions 

 connected with the senses of sight, touch, hearing, and 

 smell. Munk's special sensorial localizations, however, 

 disagreed with Terrier's ; and Goltz, from his extirj)ation- 

 experiments, came to a conclusion adverse to strict local- 

 ization of any kind. The controversy is not yet over. I 

 will not pretend to say anything more of it historically, but 

 give a brief account of the condition in which matters at 

 present stand. 



The one thing which is perfectly well established is this, 

 that the ' central ' convolutions, on either side of the fissure of 

 flolando, and (at least in the monkey) the calloso-marginal 

 convolution (which is continuous with them on the mesial 

 surface where one hemisphere is applied against the other), 

 form the region by which all the motor incitations which 

 leave the cortex pass out, on their way to those executive 

 centres in the region of the pons, medulla, and sj^inal cord 

 from which the muscular contractions are discharged in 

 the last resort. The existence of this so-called 'motor 

 zone ' is established by the lines of evidence successively 

 given below : 



(1) Cortical Irritations. Electrical currents of small 

 intensity applied to the surface of the said convolutions in 

 dogs, monkeys, and other animals, produce well-defined 

 movements in face, fore-limb, hind-limb, tail, or trunk, 

 according as one point or another of the surface is irritated. 

 These movements affect almost invariably the side opposite 

 to the brain irritations : If the left hemisphere be excited, the 

 movement is of the right leg, side of face, etc. All the objec- 

 tions at first raised against the validity of these experiments 

 have been overcome. The movements are certainly not due 

 to irritations of the base of the brain by the downward spread 

 of the current, for : a) mechanical irritations will produce 

 them, though less easily than electrical ; b) shifting the 



