PRACTICAL CONSIDERATIONS : THE BRAIN. 



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of touch ; he calls it the somcesthetic area. It includes the precentral and postcentral 

 convolutions, the paracentral lobule. The sensory fibres passing from the periph- 

 ery to this area would appear to excite sensations of touch, pain, temperature, 

 muscle- and tendon-sense, equilibrium, etc. This cortical region probably repre- 

 sents a complex mass of sense centres rather than a single sensory area, and in 

 addition to being a sensory field, the somaesthetic area is the great motor region 

 of the brain. 



When this sensory-motor area and the various sensory areas are fully taken into 

 account, there still remain about two-thirds of the cortex which appear to have noth- 

 ing to do with the periphery. Flechsig calls these regions of the cortex ' ' associa- 

 tion centres, " as he believes they furnish arrangements for uniting the various central 

 sense areas. 



The best known cortical areas are the motor, speech, visual, and auditory, al- 

 though new contributions to our knowledge are being made from time to time. Re- 

 cently Griinbaum and Sherrington have demonstrated in the cortex of the higher 

 apes, including the orang and several species of the chimpanzee and gorilla, that the 

 motor area was found in the whole length of the precentral convolution and the en- 



FIG. 1041. 



Left cerebral hemisphere illustrating diagrammatically motor zone and its subdivisions. (Mills.) 



tire length of the central fissure. It did not at any point extend behind the central 

 fissure. They demonstrated other important facts in connection with this and other 

 areas. These results have been in part at least confirmed by recent histological re- 

 searches, and by faradization of the human brain during operation for the purpose 

 of more accurately identifying the relations of the opening to the area to be exposed. 



The most important, because the best known, area of the cortex, is that asso- 

 ciated with the fissure of Rolando and the fissure of Sylvius. 



Before the publication of the experiments and observations just alluded to, the 

 motor zone was regarded as extending over both central convolutions which lie one 

 anterior and the other posterior to the central fissure or fissure of Rolando, also over 

 the paracentral lobule on the median aspect of the hemisphere, and to some extent 

 into the posterior extremities of the first and second convolutions. The trend of 

 opinion is now in favor of the view that the motor region is entirely or almost en- 

 tirely in front of the central fissure (Monakow, Mills). This is, of course, a matter 

 of considerable importance in trephining for a tumor or hemorrhage supposed to be 

 situated in this area, as instead of making the opening directly astride of the fissure 

 of Rolando it would be better, if these views are correct, to operate with the idea of 

 exposing a region two-thirds or three-fourths in front and one-third or one-fourth 

 behind the central fissure. 



