704 THE BRAIN. 



anatomical leading fails, as in hearing and taste. In the case of sensations 

 of the body at large, the anatomical leading similarly fails. Moreover, any 

 attempt to push the analogy of sight raises the following question : If there 

 were two optic nerves on each side of the head, would there be two cortical 

 areas, one for each nerve, in each hemisphere, or one visual area only ? And 

 again, if the optic nerve were the instrument for some sense in addition to 

 that of sight, would there be two cortical areas, one for each sensation, or 

 one area only serving as the cortical station, so to speak, of the whole nerve ? 

 If we push the analogy of sight it is open for us, since we cannot give a 

 definite answer to the above question, to suppose either that there is one area 

 for touch, another area for temperature, and so on, each for the whole body, 

 or that there is an area for sensations of all kinds for each afferent nerve, or, 

 that there is an intricate arrangement which supplies all the combinations of 

 the two which are required for the life of the individual. Of the three 

 hypotheses the latter is the more probable; but if so, it is by its very nature 

 almost insusceptible of experimental proof, especially when we bear in mind 

 what we have already said touching the difficulty of judging the sensations 

 of animals. If the judgment of visual sensations is difficult, how much more 

 difficult must be the judgment of sensations of touch and temperature? 

 Indeed, sensations of pain are the only sensations of which we can form a 

 quantitative judgment in animals ; and our method of judging even these, 

 namely, by studying the movements or other effects indirectly produced, is a 

 most imperfect one. 



We can learn, therefore, almost absolutely nothing in this matter from 

 experimental stimulation of the cortex in animals. As we have previously 

 ( 584) urged, the absence of movements when parts of the cortex other than 

 the motor regions are stimulated 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 shown in many ways, for example by 

 the experiment, described in 574, 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 in- 

 terpreted with clearness and certainty. In the monkey removal or destruc- 

 tion of the gyrus fornicatus (Figs. 148 and 150) 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 dif- 

 ficulty), has brought the whole of the opposite side of the body to a condition 

 which has been described as an anaesthesia, 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 move- 

 ments and, though apparently diminishing as time went on, lasting until the 

 death of the animal some weeks afterward. Again, removal of the contin- 

 uation of the gyrus fornicatus into the gryus hippocampi has, in other in- 

 stances, led to a more transient anaesthesia 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 show that in man, when mischief 

 apparently limited to the cortex produces loss of sensation, it is the parietal 



