CHAP.X.] COURSE OF THE NERVOUS POWER IN THE BRAIN. 291 



which its colouring matter and its fibrine are found in small 

 quantity, is very favourable to the effusion of fluid into the ven- 

 tricles. 



It may serve, in some degree, to convey a clearer general idea of 

 the anatomy of the brain, if, in conclusion, we explain the course 

 which the nervous force might, and probably does follow, when 

 developed in any particular segment of this complex organ. 



If we suppose the source of power to be the convolutions 011 

 either side, the nervous force would be propagated by the fibres of 

 the hemisphere to the vesicular matter of the corpus striatum ; 

 from which it would pass along the fibres of the inferior layer of 

 the crus cerebri, through the mesocephale, to the anterior pyramids 

 of the medulla oblongata ; along which it would be conveyed to 

 the opposite half of the spinal cord, exciting the nerves which 

 spring from that segment. Supposing this to be the route in which 

 the impulse of volition is propagated to the muscles, it becomes 

 very easy to understand why a state of paralysis must ensue, when 

 an apoplectic clot, or other morbid deposit in any part of the 

 course above described, compresses or ruptures the fibres, or when 

 a state of softening destroys their vital powers, or causes a solu- 

 tion of their continuity. If the seat of disease be in the white 

 matter, the channels along which the nervous power travels will 

 be interrupted ; if it be in the gray matter, the sources of nervous 

 power are impaired. In all cases the extent of the paralysis will 

 be proportioned to that of the lesion, and for the most obvious 

 reasons. 



If the cerebellum be the source of power, the nervous force will 

 travel from either hemisphere along the fibres of the crus, and by 

 those of the restiform body to the spinal cord, and from the conti- 

 nuity of the former with the posterior column of the latter it is 

 probable that this column would be more immediately excited. 



So little is known of the precise channels through which im- 

 pressions created at the periphery are propagated in the central 

 organ, that we can hardly do more than speculate on the subject. 

 We may, however, fairly conclude, that those segments with which 

 nerves admitted to be sensitive are in close connexion, must be 

 instrumental in the propagation of the nervous power, when excited 

 by sensitive impressions ; and hence we are led to assign to the 

 olivary columns of the medulla oblongata, and their continuations 

 in the mesocephale, with the optic tubercles and the thalami, a 

 considerable share in this office, inasmuch as the auditory, the 

 fifth, and the optic nerves, are intimately connected with them. 



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