SIR CHARLES BELL ON THE BRAIN. 481 



nerves in the axilla, and in the loins, what combines the muscles of the trunk, and 

 more especially what joins the extremities together in sympathy ? That these com- 

 bined motions and relations are not established in the brain, the phenomena exhibited 

 on stimulating the nervous system of the decapitated animal sufficiently evince. They 

 must therefore depend on an arrangement of fibres somewhere in the spinal marrow. 

 Comparative anatomy countenances this idea, since the motions of the lower ani- 

 mals are concatenjited independently of a brain, and independently of the anterior 

 ganglion, which in some respects gives direction to the volition of these animals. 



It comes next to be inquired what use there can be in a decussation, by which one 

 side of the brain is made to serve the opposite side of the body. Ingenuity can offer 

 no reason for such an arrangement ; the object nmst surely be an interchange of 

 fibres, and consequently a correspondence in the movements of the sides of the body 

 and of the extremities. And on this subject it must be admitted, that although in 

 nine out of ten cases the side of the body opposite to that which is diseased in the 

 brain is affected with paralysis, it is not always so, and very often a certain debility 

 is perceptible in the side which is least affected. Again, when a man is seized with 

 paralysis, he is sometimes at the instant affected with pain in the other side. These 

 irregularities tend to countenance the belief that the decussations of the sensitive and 

 motor spinal columns are rather intended to effect combination and sympathy between 

 every part of the frame, than that one half of the brain should belong to the opposite 

 half of the body, for no apparent object, and without producing any harmony of action. 



Such arguments induce me to believe that the brain does not operate directly on 

 the frame of the body, but through the intervention of a system of nerves whose 

 proper roots are in the spinal marrow, and that the decussation, or rather the ar- 

 rangement of the fibres, takes place at the point where the columns descending from 

 the brain join the spinal marrow, and consequently in effect above the origin of all 

 the nerves, excepting those of the four senses. This supposition would furnish an 

 explanation of the whole of one side of the body, limbs, face, and head, being similarly 

 affected in paralysis. It would also explain the appearance, which all the nerves of 

 motion and sensibility have, of coming in a direction upwards from the spinal marrow, 

 rather than directly outwards from the brain, as the nerves of the proper organs of 

 sense do. 



In reflecting on the origins of the nerves of the encephalon, it appears that neither 

 nerves of sense nor of motion arise from the cerebellum or its processes. It further 

 appears that the restiform bodies or processes form no union or decussation similar 

 to those which we have described in the columns of motion and sensation which de- 

 scend from the cerebrum. 



Those descending processes of the cerebellum, however, form a large portion of the 

 spinal marrow ; and we must thence infer that the cerebellum operates through the 

 system of the spinal marrow. 



