FUNCTIONS OF THE BRAIN 



951 



starting-point of a long series of researches by Ferrier, Munk, Horsley, 

 Schafer, Heidenhain, and many others, on the brains of monkeys as 

 well as dogs researches which have formed the basis of an exact 

 cortical localization in the brain of man, and have enriched surgery 

 with a new province. In these later experiments the interrupted cur- 

 rent from an induction machine has been found the most suitable form 

 of stimulus (see Practical Exercises, p. 1001), especially when one elec- 

 trode only is placed on the cortex and the other on some indifferent 

 part of the body e.g., in the rectum (unipolar stimulation), a pro- 

 cedure which permits of finer 

 localization than when both 

 electrodes are applied to the 

 brain (bipolar stimulation). 



' Motor ' Areas.* These 

 have been localized 

 with great care (both by 

 stimulation and by removal 

 of portions of the cortex) 

 in the brains of the higher 

 apes (gorilla, orang, and 

 chimpanzee) by Sherrington 

 and Griinbaum, and there 

 can be no doubt that the 

 results, in their general 

 outlines at least, qan be 

 applied to the human brain. 

 These observers employed 

 the so-called unipolar 

 method of stimulation. 



The ' motor ' region in- 

 cludes the whole length of 

 and the whole of the free 

 width of the precentral 

 or ascending frontal con- 

 volution, and dips down to 

 the bottom of the central 

 sulcus (fissure of Rolando 

 in man), but does not 

 extend behind the sulcus. It extends also into the depth of all the 

 fissures, so that the hidden part of the excitable area probably 

 equals, perhaps exceeds, the part which is free on the surface of the 

 hemisphere. The anterior limit of the ' motor ' field is not quite 



* Since the so-called ' motor ' area, as is now well known, is really sensori- 

 rnotor, and a region having to do purely with the discharge of motor impulses 

 does not exist, it would be better to call it the sensori-motor, or, following 

 Bastian's suggestion, the kinaesthetic area. Probably, however, the altera- 

 tion of a term so long sanctioned by custom in physiological writings would 

 lead to confusion. Accordingly, in what follows the word ' motor ' will be 

 retained, but to show that it is used in a special sense it will be enclosed in 

 quotation marks. 



Fig. 383. Dog's Brain with Lesion. A portion 

 of the cortex indicated by the shaded area 

 was destroyed by cauterization. The symp- 

 toms were complete blindness of the opposite 

 eye (in this case the right); weakness of the 

 muscles of the limbs and of the neck on the 

 right side; slight weakness of the limbs on the 

 left side. When the animal walked, there was 

 a tendency to turn to the left in a circle. In 

 eating or drinking, the head was turned to the 

 left, so that the mouth was oblique, and the 

 right angle of the mouth was lower than the 

 left. The tail movements were normal, and 

 there was no deviation of the tail to one side. 



