THE CENTRAL NERVOUS SYSTEM 



843 



tions on man, and partly from the results of the removal or 

 stimulation of definite areas in animals. And so varied and 

 extensive have been the contributions from both of these 

 sources, that it is difficult to decide to which we owe most. 

 In addition, the study of the development of the myelin sheath, 

 and especially in recent years the minute study of the histology 

 of the various regions, have aided materially in mapping out 

 the cortex. 



It is a fact which might appear strange and almost inexplicable 

 did the history of science not constantly present us with the like, 

 that forty years ago the 

 universal opinion among 7L 



physiologists, pathologists, ^JB i FBhrt V 



and physicians was that fl^ ^r IN" Sk.' n 

 the cerebral cortex is in- 

 excitable to artificial 

 stimuli, that no visible 

 response can be obtained 

 from it. The great names 

 of Flourens and Magendie 

 stood sponsors for this 

 error, and repressed re- 

 search. In 1870, however, 

 Hitzig and Fritsch showed 

 that not only was it pos- 

 sible to elicit muscular 

 contractions by stimula- 

 tion of the cortex of the 

 brain in the dog with vol- 

 taic currents, but that the 

 excitable area occupied a 

 definite region in the neigh- 

 bourhood of the crucial 

 sulcus or sulcus centralis, 

 which runs out over the 

 convexity of the hemi- 

 spheres nearly at right 

 angles to the longitudinal 

 fissure. In this region 

 they were further able to hemisphere, 

 isolate several distinct 

 areas, stimulation of which was followed by movements respectively 

 of the head, face, neck, hind-leg, and fore-leg (Fig. 349). This was 

 the 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 current from an induction machine has been found 

 the most suitable form of stimulus (see Practical Exercises, p. 889), 

 especially when one electrode only is placed on the cortex and 

 the other on some indifferent part of the body e.g., in the rectum, 

 (unipolar stimulation), a procedure which permits of finer localiza- 

 tion than when both electrodes are applied to the brain (bipolar 



FIG. 349. MOTOR AREAS OF DOG'S BRAIN. 



n, neck ; /./., fore - limb ; h.l., hind - limb ; 

 t, tail; /, face; c.s., crucial sulcus; e.m., eye 

 movements ; p, dilatation of the pupil in both 

 eyes, but especially in the opposite eye. All 

 the areas are marked in the figure only on the 

 left side except the eye areas, whose position, 

 to avoid confusion, is indicated on the right 



