94 Post central Gyrus in a Case of Caps alar Lesion [CHAP. 



postcentral gyrus, to the Rolandic wall and lip, to the field which was mapped out long before 

 this pathological investigation was thought of, by its possession of a very curious and destruc- 

 tive structure, the field which I have sometimes distinguished by the name postcentral area 

 proper. Out of this the question arises, Does this small and narrow strip of cortex represent 

 all the brain surface which has to deal with the reception and final elaboration of common 

 sensory impulses ? The reply is in the negative, for, in discussing the various factors which 

 contribute to the perfection of " common sensation," it will be pointed out that these components 

 are divisible into two categories, the first of which we will for convenience call fundamental 

 components, and the second psychic ; and reasons will be given for believing that the cortex behind 

 the postcentral area proper that is, the cortex of the intermediate postcentral area, and possibly 

 of the parietal lobe bears a psychic function. But this introduces a difficulty, because in 

 Tabes Dorsalis we know that sensation is impaired in all its components, psychic as well as 

 fundamental, and, this being so, why does not the supposed psychic cortex also undergo changes ? 

 In endeavouring to explain this -apparent anomaly we must turn to other sensory areas and 

 see what takes place in them in cases of peripheral interruption of the conducting path for 

 their stimuli. Take the visual area as an instance : in cases of blindness from any cause, the 

 part on which the cortical change falls with greatest intensity is the calcarine area, the field 

 on which visual impressions are believed to primarily impinge, and which we call visuo-sensory ; 

 and it also appears, although it cannot be taken as proved, that the change begins in this 

 area, and that the alterations which affect cells in the investing visuo-psychic cortex follow at 

 a much later date, in addition to being less severe and less readily demonstrated. Now I 

 venture to think that the analogy can be extended to the changes in the postcentral cortex 

 in Tabes Dorsalis. Destruction of terminal and fundamental cells, which the sensory neurones 

 first strike in the postcentral area proper, occasions loss or impairment of all forms of sensation, 

 but the cells subserving a psychic function, placed in areas further back, only having indirect 

 associations with these neurones, are more resistive to decay, also, not being so concentrated 

 in their deposition as the primary sensory elements, their degeneration does not bring in its 

 train such a manifest general disturbance of cell-lamination. 



Another question arising from the findings in Tabes Dorsalis is whether common sensations 

 emanating from different parts of the body are delivered at levels in the postcentral gyrus 

 which correspond in position and in sequence with those which are known to dominate move- 

 ments of given groups of ncmscles. From clinical experience, and from some evidence which 

 I shall bring forward in describing the cortical changes in cases of amputation, it seems that 

 this is the case, and I have little doubt that tabetic material could be used to advantage in 

 the settlement of the point. Thus it is conceivable that many interesting details would be 

 forthcoming from an examination of the brain in a series of cases exhibiting stress of spinal 

 affection at different levels. For a rougher localisation, cases of transverse myelitis might 

 prove valuable. 



Postcentral Gyrus in a Case of Old-standing Gapsular Lesion. 



In the following case the microscopic examination aimed at the display of the cortical 

 changes arising from interruption of the sensory chain of neurones at the level of the internal 

 capsule, as well as the determination of the distribution of the same on the surface of the 

 brain. 



