646 MANUAL OF PHYSIOLOGY. 



6. Stimulation of the convolutions around the fissure of Rolan- 

 do, however, gives rise to definite coordinated movements of 

 muscles of the other side of the body. Indeed, local groups of 

 muscles respond with surprising constancy to the electric stimu- 

 lation of certain definite parts of the cortex. These convolu- 

 tions have thus been mapped out into motor centres for hind 

 limb, fore limb, face, etc. 



From this we are tempted to conclude (1) that the cortex of 

 the posterior region of the hemispheres is related to the reception 

 of some sensory impressions ; (2) that the superior and lateral 

 part in the neighborhood of the fissure of Rolando is related to the 

 discharge of voluntary motor impulses ; and (3) that the anterior 

 lobes are not immediately subservient to either the sensory or 

 motor functions of the hemispheres, though the centre presiding 

 over the faculty of speech is placed in this part on the left side. 



As an objection to the soundness of these conclusions, the 

 remarkable and undoubted fact has been urged, that no matter 

 how thorough is the destruction of the centres, the function 

 returns after the lapse of a variable interval. In some instances 

 the loss of function only remains for a few hours after the opera- 

 tion ; in other cases (those in which the injury is extensive and 

 deep, and the animal belongs to a class with high mental organi- 

 zation) the recovery is slow and may extend over several weeks 

 and months. In man and monkeys the function may be lost 

 forever, and the nerve channels, which formerly carried the im- 

 pulses to or from the injured centre, become degenerated. 



From some of the foregoing facts viz., the constant and 

 regular response of certain groups of muscles to the stimulation 

 of certain local spots of the brain surface, and the temporary 

 destruction of the functions of some organ when a certain point 

 is injured it seems definitely fixed that certain local parts of the 

 brain surface are in more immediate connection with certain 

 peripheral organs than are others, and that these local areas have 

 been in the habit of receiving (in the case of the visual impulses 

 coming to the angular gyri) or sending out (in the case of motor 

 impulses starting from the motor centres) impulses of a special 

 and definite kind. 



