LESION OF DIFFERENT REGIONS OF THE CEREBRAL HEMISPHERES. 563 
and the hippocampal region only partially involved, there was only slight and transitory 
impairment of tactile sensibility on the opposite side. 
These, as well as other similar facts narrated, serve to show that the lesions of the 
lower temporo-sphenoidal region which are necessarily made in attempts to destroy the 
hippocampal region from the external aspect of the temporal lobe are negative or 
unimportant in the causation of the anaesthesia. 
Where the hippocampal region was reached through or from the under surface of the 
occipital lobe, and particularly in the former case, where the medullary fibres of the 
whole of the posterior lobe were invaded, tactile anaesthesia was complicated with visual 
defects more or less pronounced. But the experiments recorded in Section I. enable us 
to eliminate the visual defects and assign them to the lesions inflicted on the occipito- 
angular region. 
The sense of hearing was very rarely affected, and then only when the lesions 
invaded the medullary fibres of the superior temporo-sphenoidal convolution. 
By thus eliminating the effects of lesions of the occipito-angular region, of the 
superior temporo-sphenoidal, and in large measure at least of the middle and lower 
temporo-sphenoidal region, we arrive at the lesion of the hippocampal region as the 
essential factor in the causation of the anaesthesia observed in the various cases. 
When the hippocampal region was entirely destroyed, as in Experiment 27, the 
most complete anaesthesia was manifested on the opposite side, and the degree of 
anaesthesia varied in other experiments with the completeness of the destruction of 
this region. 
In some of the experiments the apparently impossible feat was accomplished of 
restricting the lesion to the gyms hippocampi and hippocampus itself respectively. 
When the cortex of the gyrus hippocampi was alone or mainly injured, as in Expe¬ 
riments 24 and 26, there was well-marked impairment of tactile sensibility on the 
opposite side, but not of permanent duration. 
When the fascia dentata and internal margin of the gyrus hippocampi were alone 
injured, as in Experiment 32, there was a remarkable hypersesthesia of a transient 
character, which has already been commented on. In another sense this fact is of 
importance as showing that the anaesthesia resulting from lesions of the hippocampal 
region cannot be explained away on any theory of mere proximity of the lesions to the 
sensory tracts of the hemisphere. For in this case the lesion was nearer the crus 
cerebri than in any of the others. 
When the cornu ammonis alone was the seat of lesion, as in the left hemisphere of 
Experiment 33, there was for a time very marked anaesthesia of the opposite side. 
But here, also, as in the cases where the gyrus hippocampi alone was injured, the 
symptoms were only of temporary duration. 
These facts, therefore, show that the hippocampus and hippocampal gyrus form 
parts of the same centre, and that complete destruction of both structures is necessary 
to secure complete and permanent anaesthesia. But to effect this primarily is both 
4 c 2 
