1092 CUTANEOUS SENSATIONS. [BOOK m. 



matter from experimental stimulation of the cortex in animals. 

 As we have previously ( 671) urged, the absence of movements 

 when parts of the cortex other than the motor region are stimu- 

 lated is no evidence that the stimulation does not give rise to 

 psychical events into which sensations enter ; and movements 

 follow stimulation of the motor area, not because that area is 

 wholly given up to motor events, but because from the histological 

 arrangement the stimulus gets ready access to relatively simple 

 motor mechanisms. That the motor region has close connections 

 with sensory factors is not only almost certain on theoretical 

 grounds, but is shewn in many ways, for example by the 

 experiment, described in 661, of exalting the sensitiveness of 

 a motor area by generating peripheral sensory impulses. 



Nor can the effects on sensation of removal of parts of the 

 cortex be interpreted with clearness and certainty. In the monkey 

 removal or destruction of the gyrus fornicatus (Figs. 125, 127) on 

 the mesial surface of the brain, ventral to the calloso-marginal 

 sulcus which forms on the mesial surface the ventral limit of the 

 motor region (an operation of very great difficulty), has brought 

 the whole of the opposite side of the body to a condition which 

 has been described as an anesthesia, that is a loss of all cutaneous 

 tactile sensations, and an analgesia, that is a loss of sensations of 

 pain, the condition being accompanied by little or no impairment 

 of voluntary movements and, though apparently diminishing as 

 time went on, lasting until the death of the animal some weeks 

 afterwards. Again, removal of the continuation of the gyrus 

 fornicatus into the gyrus hippocampi has in other instances led 

 to a more transient anesthesia also of the whole or greater part 

 of one side of the body. And it is asserted that removal of no 

 other region of the cortex interferes with cutaneous and painful 

 sensations in so striking and lasting a manner as does the removal 

 of parts, or of the whole of this mesial region. 



These results, however, do not accord with clinical experience, 

 which, though scanty, seems as far as it goes to shew that in man, 

 when mischief apparently limited to the cortex produces loss of 

 sensations, it is the parietal lobe corresponding to the motor region 

 which is affected ; but there appears to be no record of any case of 

 a cortical lesion affecting sensation without affecting movement. 

 We have previously called attention to the fact that the temporary 

 loss or impairment of movement which follows removal of an area 

 is frequently, if not always, accompanied by an impairment of 

 cutaneous sensations in the limb or part * paralysed ' ; and side by 

 side with this we may put the experience that in the human 

 epileptiform attacks of cortical origin, the seizure is at times 

 ushered in by peculiar sensations, called the 'aura/ in the part 

 movements of which inaugurate the march of convulsive move- 

 ments. But these things do not shew that the cortical area is the 

 "seat of sensations," they rather illustrate what we said concerning 



