530 ELEMENTARY PHYSIOLOGY less. 



electrically close to the fissure of Rolando along its 

 anterior margin, very definite movements take place in 

 the limbs of the opposite side of the body. If care is 

 taken to localise the stimulation as far as possible witliin 

 the limits of a small area of the cortex tlie resulting move- 

 ments are found to l)e limited to a correspondingly small 

 group of muscles of the limb affected. Again, if that 

 piece of cortex whose stimulation gives rise to movements 

 be cut out or extirpated, tlie animal so operated on is 

 found to have lost the power of executing this particular 

 set of movements. The outcome of such experiments 

 makes it clear that the cerebral cortex along the course of 

 the fissure of Rolando is concerned in the develoj^ment of 

 muscular movements ; hence the name of " motor areas " 

 was given to these parts of the cortex. Our knowledge 

 of the existence and position of these areas as derived 

 from experiments on animals is moreover completely con- 

 firmed by the observation of the results of Nature's own 

 experiments on man ; as for instance by an examination 

 after death of the brains of patients who during life had, 

 as the result of cerebral disease, exhibited symptoms 

 similar to those obtainable by stimulation or extirpation 

 of cortical areas in animals. 



Proceeding in a similar way it has been further found 

 that certain portions of the cortex are peculiarly connected 

 with the development of sensations, so that we come to 

 speak also of "sensory areas." In this case observations 

 on man are specially instructive, since the patient can 

 give an account of his sensations, whereas another animal 

 cannot. 



One of the earliest known and most interesting cases of 

 localisation of function in the cerebral cortex is that of 

 the centre for speech. Some long time before experi- 

 ment revealed the existence and position of the centres to 

 which we have so far referred it was noticed by a French 

 physician named Broca that patients who had exhibited a 

 curious inability to pronounce definite words or syllables 



