104 Remarks OH Common Sensation [CHAP. 



Having offered these explanatory remarks, we can now enquire what evidence on tactile 

 localisation clinical observation has supplied. Now, for reasons previously mentioned, it would 

 be profitless to select for analysis those cases of lesions in the Rolandic zone which, according 

 to records, are believed to have been limited to the postcentral gyrus ; but I must say that in 

 a comprehensive survey of a number of instances finding a place in the literature, I have been 

 struck by reading that when a lesion causing motor palsy has been so situated as to attack 

 the motor (precentral) area from the frontal side there has been an entire absence of sensory 

 change ; when, again, the lesion has been placed in the parietal lobe away from the postcentral 

 area the simple recognition of touch has been uninfluenced (the same does not apply to the 

 localisation of the same) ; but when, on the other hand, the lesion has directly involved the 

 postcentral gyrus, the sensory defect has been plainly in evidence. 



And, while the question is far from closed, and I shall be much interested to hear the 

 result of more thorough investigation on this point, it cannot be denied that this evidence, 

 along with the histological data already set forth, favour the assumption that the arrival 

 platform for the tactile impression is the postcentral gyrus, and, introducing an analogy, I would 

 compare the tactile with the visual centre, and as this centre is divided into a primary 

 sensory, and psychic part, so also I would divide that ; and I would regard the cortex covering 

 the wall and lip of the Rolandic fissure as a primary field for the reception, and the reception 

 only, of crude sensory impulses (modified, perhaps, by passage through subordinate nuclei, just 

 as visual impressions may be modified by passage through the internal geniculate bodies) ; then 

 the further elaboration of the crude tactile stimulus, that is, the psychic process involved in 

 its localisation and the formation of a judgment as to its nature, and of other more involved 

 senses (stereognosis and the muscle sense), in which the tactile sense forms part of a combination, 

 I would delegate to the investing intermediate postcentral cortex and parietal lobe. In accordance 

 with this view, it would follow as a matter of necessity that destruction of the primary centre 

 (the postcentral area proper in my scheme) would bring in its train impairment, not only of 

 the tactile sense, but also of the other senses which it assists to perfect, and, on the other 

 hand, a lesion outside the postcentral area proper would evoke disturbances of the psychic 

 component in the various senses without interfering with the simple component in tactile sense. 

 While some few clinical cases may be found to contradict this hypothesis, I think it harmonises 

 with the generality of observations. It also seems to be in agreement with my cortical 

 findings in Tabes Dorsalis, because, although in this disease there is no variety of common 

 sensibility which does not suffer impairment as the condition advances, anaesthesia to tactile 

 impressions is the opening phenomenon in the train of sensory changes 1 , and, as I have 

 already described, the cortical changes are concentrated in the cortex of the postcentral area 

 proper. 



The Muscular Sense". 



This sense, so necessary to the coordination of voluntary movement, because it is the 

 sense by which we appreciate the position and condition of our muscles, is of special interest 

 to the student of localisation, because its disturbance causes a readily recognised disability, 

 and its impairment has been noted over and over again in cases of surface lesion. Now 



1 According to Mott " trunk anaesthesia to light tactile impressions is the earliest and most constant sensory 

 disturbance," and fails in the preataxie stage only. 



In not one of the 49 cases examined by Forster and Friinkel was skin sensibility normal. 



- The muscle sense must be a combination of the sensations proceeding from skin, muscles, tendons, and joints. 



