730 



FUNCTIONS OF THE CEREBRUM 



[CH. L. 



Some diseases, on the other hand, act as the induction currents 

 do in artificial stimulation ; they irritate the surface of the brain ; 

 such a disease is a tumour growing in the membranes of the brain ; 

 if the tumour irritates a piece of the motor area, there will be 

 involuntary movements in the corresponding region of the body; 

 these movements may culminate in the production of epileptiform 

 convulsions commencing in the arm, leg, or other part of the body 

 which corresponds to the brain area irritated. It is these cases of 

 " Jacksonian Epilepsy " which have given the best results in surgery ; 

 the movement produced is an indication of the area of the brain 

 which is being irritated, and the surgeon after trephining is able to 

 remove the source of the mischief. If the area of the brain which 

 is irritated is a sensory area, the result produced is a subjective 

 sensation, similar to what we imagine is produced in animals with 

 an electric current. 



We may now proceed from these general considerations to 

 particular points, and give maps of the brain to show the areas we 

 have been speaking of. 



Fig. 448 is a view of the dog's brain. It is convenient to take 

 this first because it was the starting-point of the experimental work 

 on the subject in the hands of Hitzig and Fritsch. If the text 

 beneath the figure is consulted, it will be seen that the motor areas, 

 mapped out by the method of stimulation, are situated in the 

 neighbourhood of the crucial sulcus, which probably corresponds to 

 the fissure of Eolando in man. 



Coming next to the brain of the monkey, figure 449 is repro- 

 duced from Ferrier's book. He marked out the surface into a 



number of circles, stimu- 

 lation of each of which 

 produced movements of 

 various sets of muscles, 

 face, arm, and leg, from 

 below upwards ; extirpa- 

 tion of these same areas 

 produced the correspond- 

 ing paralysis. It will be 

 further noticed that these 

 areas are all grouped 

 around the fissure of 

 Eolando, particularly in 

 the ascending frontal con- 

 volution. 



Much of our knowledge concerning the localisation of the motor 

 area in the human brain has been deduced from experiments on the 

 lower monkeys. Valuable as such knowledge is, infinitely more 



FIG. 449. 



