iv] r<>stn'ntr<tl or Si'iixort/ Area 107 



Senses of Pain and Temperature. 



\Ye have now discussed the senses which are most commonly the subject of affection, 

 which are frequently involved in association with one another, and which may in certain 

 instances be totally in abeyance. The two remaining senses, those tor the recognition of 

 impressions of pain, and of heat and cold, differ from the foregoing in being never completely 

 lost although liable to impairment in cases of cortical lesion. 



In reference to tile sense of pain, Goltz demonstrated, many years ago, that even in 

 a. decerebrate condition an animal reacted with livelier movements than before to stimuli 

 normally provocative of pain, and he formulated untenable views which need not be entered into 

 here. Munk, pursuing the subject further, found that after removal of the regio sigmoidea 

 in the dog and the production of loss of general sensibility, the animal still appreciated 

 painful stimuli; he so confirmed Goltz's observation; but in explaining his finding he maintained 

 that although the dog felt pain it was unable to locate the irritant or tell its nature, in 

 other words, the disability affected conscious perception and not common sensibility. It appears 

 that the same holds good in the human being, for it is a well-recognised truth that 

 hemianaesthetic individuals in whom the sense of touch is almost abolished are still susceptible 

 to pain, but do not orientate it correctly. 



The part of the brain surface serving for the direct reception of sensations of pain and 

 temperature is no more definitely known than that standing in relation with the other senses, 

 but as they, like the first component in the tactile sense, are simple in character, it is 

 probable that they are primarily represented in the postcentral area proper ; it is also likely 

 that they undergo modification in the intermediate stations of the sensory chain of neurones. 



SUMMARY. 



The line of argument throughout this chapter is directed towards proving that the post- 

 central gyrus constitutes the terminus where the main system of fibres for the conveyance of 

 impressions pertaining to tactile and allied forms of sensation primarily impinges. 



Structurally it differs entirely from the precentral gyrus, and from the superior parietal 

 and supramarginal convolutions : and its definition as a distinctive area is accomplished 

 without the slightest difficulty. Concerning its supply of nerve fibres, it is not nearly so 

 richly endowed as is the precentral gyrus, and a most important distinguishing feature is the 

 presence in the interradiary plexus of fibres of even larger calibre than those seen in the 

 precentral convolution, fibres which are curious inasmuch as they run obliquely or at right 

 angles to the radiating fasciculi. 



Such fibres recall some met with in known sensory regions, for instance, the visual, 

 auditory, and olfactory centres. They are not seen in either the precentral convolution or the 

 parietal lobe proper, they seem to concentrate themselves on the Rolanclic side of the gyrus, 

 and their curious oblique course gives rise to the assumption that they are centripetal fibres 

 making for cells resident in this situation. 



In reference to nerve cells the lamination differs from that of the precentral gyrus, first, 

 in showing no true cells of Betz ; and, secondly, in exhibiting a most pronounced layer of 



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