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t are perhaps the following. Besides the regions instanced above, in the limbic (olfactory), occipital (visual), and temporal (auditory) lobes, as exhibiting precocity of development, there is a region showing similar precocity in the fronto-parietal portion of the hemisphere. This is the region which in the Primates includes the large _central fissure_ (sometimes called the fissure of Rolando). To it fibres are traced which seem to continue a path of conduction that began with afferent tracts belonging to the spinal cord, and tracts which there is reason to think conduct impulses from the receptor-organs of skin and muscles. The part of the cortex immediately behind the _central fissure_ seems to be the main cortical goal for these upward-conducting paths. That _post-central_ strip of cortex would in this view bear to these paths a relation similar to that which the occipital and temporal regions bear to afferent tracts from the retina and the cochlea. There are observations which associate impaired tactual sense and impaired perception of posture and movement of a limb with injury of the _central region_ of the cortex. But there are a number also which show that the motor defect which is a well-ascertained result of injury of the _pre-central_ gyrus is sometimes unaccompanied by any obvious defect either of touch or of muscular sense. It seems then that the motor centres of this region are closely connected with the centres for cutaneous and muscular sense, yet are not so closely interwoven with them that mechanical damage inflicted on the one of necessity heavily damages the other as well. There is evidence that the sensory cortex in this region lies posterior to that which has been conveniently termed the "motor." These latter in the monkey and the man-like apes and man lie in front of the central fissure: the sensory lie probably behind it. A.W. Campbell has found changes in the cortex of the post-central convolution ensuing in the essentially sensory disease, _tabes dorsalis_, a disease in which degeneration of sensory nerve-fibres of the muscular sense and of the skin senses is prominent. He considers that in man and the man-like apes the part of the post-central gyrus which lies next to and enters into the _central fissure_ is concerned with simpler sensual recognitions, while the adjoining part of that convolution farther back is a "psychic region" concerned with more complex psychosis connected with the sense
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