794 



THE CENTRAL AXIS OF THE NERVOUS SYSTEM. 



the study of the nerve-centres ; for on a perfect knowledge of it depends the 

 solution of the most difficult problems in the physiology of the nervous system. 

 Numerous attempts have been made to elucidate its intimate organization ; but 

 we must here omit the multitude of secondary details revealed by these researches, 

 and limit ourselves to the essential and fundamental facts. 



The tivo nerve-substances enter into the texture of the cerebral hemispheres, 

 and both are exactly disposed as in the cerebellum. 



The grey substance extends over the entire external surface of the brain, and 

 is prolonged into the plaits — thereby augmenting the extent of that surface, and 

 so forming the cortical layer of the cerebral convolutions. Gratiolet has compared 

 this layer to a ring-purse opening on the internal face of the hemisphere, having 

 for its rings the convolutions of the hippocampus and corpus callosum, in which 

 is included the white medullary substance. 



The grey matter projects into the lower face of the olfactory lobes and 



Fig 437 



COURSE OF ONE PORTION OF THE ASSOCIATION NERVE-FIBRES IN A HEMISPHERE. (DIAGRAMMATIC.) 



interior of the hemispheres, where it forms the central ganglia known as the 

 claustrum, lenticular nucleus, and caudate nucleus. 



In order to study the distribution of the central grey masses, horizontal and 

 vertical sections must be made of the brain, through the coi'pora striata. In 

 a vertical section by the optic commissure (Fig. 436), will be seen the caudate 

 nu/^hus limiting outwardly the lateral ventricle, and separated from the lenticular 

 nucleus by a layer of white substance — the internal capsule; between the 

 lenticular nucleus and the cerebral cortex there is a certain amount of white 

 matter. If the section is made a little more behind, there will be observed, 

 between the grey matter and the lenticular nucleus, a small greyish band named 

 the claustrum ; this is separated from the lenticular nucleus by the external capsule. 



To sum up, it is easy to perceive that the distribution of the central grey 

 masses {Jenticulo-striated bodies) is subordinate to the internal capsule. Otherwise, 

 this plays a considerable part in the physiology of the hemispheres. 



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