THE LOCALISATION OF TACTILE SENSIBILITY. 767 



Horsley and myself that extensive lesions might be made in the 

 hippocampus major without producing hemiansesthesia, although in 

 other cases, when the lesion was more extensive and involved the 

 greater part of the hippocampal gyrus, and a large part of the adjacent 

 under surface of the temporal lobe, hemiansesthesia was very marked. 

 The same result was obtained on destruction of the gyrus fornicatus, so 

 that we were led to the conclusion that these convolutions, which form 

 the greater part of the limbic lobe (especially the gyrus fornicatus) 

 were the seat of perception of cutaneous sensations, and especially of 

 tactile sensibility. Our experiments upon the gyrus fornicatus were 

 confirmed by Munk, 1 who was, however, of opinion that the anaesthesia 

 is the effect of unavoidable injury to the neighbouring Eolandic (motor) 

 region of the cortex, in which alone he localises tactile perceptions. 

 Neither did we ourselves, however, nor Terrier, ever obtain anaesthesia 

 on directly injuring the motor cortex solely. Nevertheless, it must 

 be borne in mind that in endeavouring to excise such deeply lying 

 portions of the cortex as the gyrus fornicatus and hippocampal gyrus, 

 it is necessary to raise up or draw aside the whole mass of the brain, 

 and it is possible that the heinianeesthesia we obtained in the experi- 

 ments upon the hippocampus and gyrus fornicatus were due not to the 

 actual injury to those parts, but to a general disturbance in the 

 functions of the whole hemisphere (perhaps of the optic thalamus), 

 which the manipulation of the brain might produce. 



In order to test this point, I have recently 2 performed experi- 

 ments on the monkey in the following manner: In a preliminary 

 operation, the whole of the leg area of the cortex, together with the 

 greater part of the remainder of the marginal convolution, was severed 

 by a sharp knife passed vertically into the cerebral substance parallel 

 with the longitudinal fissure. The only symptom produced was motor 

 paralysis of the opposite leg ; no anaesthesia could be detected ; the 

 animal responded, after the first day or two, to the slightest touch, both 

 on the paralysed and on the non-paralysed side. After two or three 

 weeks the brain was again exposed, and a cut was made along the same 

 line as before, but deep enough to sever the fibres passing to and from 

 the gyrus fornicatus. No additional symptoms whatever followed this 

 second operation, although in two cases at least, from one-third to one-half 

 of the gyrus fornicatus was severed from the rest of the brain. The 

 experiment was, in one case, varied by removing the gyrus marginalia 

 altogether in the first operation, and scooping away the middle part of 

 the gyrus fornicatus in the second, but the result was the same. 



These experiments are not conclusive, because the destruction of the 

 gyrus fornicatus was not by any means complete, but, so far as they 

 go, they are not in favour of this convolution being regarded as 

 especially the seat of tactile sensibility ; at least they tend to show that 

 sensation is not localised to it. It is, however, possible that the whole 

 of the limbic lobe, with the exception of the antero-inferior parts (which 

 are probably devoted to smell and taste) may be the seat of cutaneous 

 perception. It is natural to expect the senses of smell and taste to be 

 in relation with that of cutaneous sensibility, since the organs of smell 

 and taste are modifications of integumental structures. It has already 

 been shown that the view of Munk, that tactile sensibility of the 



1 Sitzungsb. d. k. Akad. d. Wissensch. zu Berlin, 1892. 



2 Journ. PhysioL, Cambridge and London, 1898, vol. xxiii. p. 310. 



