668 FUNCTIONS OF THE SPINAL CORD [CH. XLVII. 



to the optic thalamus of the opposite side, and thence by the posterior 

 part of the internal capsule to the Eolandic area of the hemisphere ; 

 the decussation of the fillet occurs in the bulb. 



Schiff, one of the earliest to work at the subject of conducting 

 paths in the cord, arrived at the conclusion that painful impressions 

 travelled to the brain by the grey matter of the cord. This conclu- 

 sion was regarded as paradoxical, for white matter is conducting, 

 grey matter is central or reflecting. But the conclusion is not so 

 paradoxical as it appears at first sight, for we now know the grey 

 matter is made up of nerve-units, communicating physiologically by 

 their interlacement of dendrons ; and it is quite easy to understand 

 that impulses may travel up grey matter through a vast series of 

 cell stations or positions of relay. The more exact methods of 

 modern research have gone far to justify Schiffs conclusions, and it 

 is now generally held that the impulses due to painful impressions, 

 and also those produced by heat and cold, travel up to the optic 

 thalamus by the loopings of fibres from cell to cell through the tract 

 of grey matter, which is continuous from cord to optic thalamus 

 (fig. 482, G.M.); from the optic thalamus the fibres of the corona 

 radiata carry on the impulse to the cortex. These conclusions are 

 confirmed by recent experiments on hemisection (see p. 619), and by 

 the phenomena seen in certain diseases. One of the most instructive 

 of these from the physiological standpoint is known as locomotor 

 ataxy. This disease is an affection of the afferent neurons, and the 

 most marked and constant change in the spinal cord is a degenerative 

 one in the posterior columns. In such a case muscular and tactile 

 sense are abolished, particularly in the lower limbs, but painful and 

 thermal sensations are felt. On the other hand, in the disease of the 

 grey matter of the cord called syringomyelia, sensations of heat, cold, 

 and pain are lost, and tactile sensations remain. 



Some afferent impulses reach the cerebellum vid the cells of 

 Clarke's column and the direct or dorsal cerebellar tract to the resti- 

 form body and inferior peduncle of the cerebellum. It terminates in 

 the vermis or middle lobe of the cerebellum ; the fibres of the tract 

 of Gowers originate in the same cells, and those of its fibres which 

 enter the cerebellum do so by its superior peduncle, and these also 

 end in the vermis. 



This leaves us still one more set of fibres to consider ; these are 

 the fibres that leave the cerebellum and travel up to the brain and 

 down the cord. They, like most of the other tracts, have been in- 

 vestigated by the degeneration method. Their exact course is, how- 

 ever, uncertain, though probably they ultimately terminate by 

 arborising round the multipolar cells of the cerebrum and of the 

 anterior horn of the cord (see fig. 482, p. 660; see also under 

 Cerebellum, Chapter XLIX.) T 



