290 



PHYSIOLOGY 



CHAP. 



cells lie in the dorsal horn ; they do not degenerate with the other 

 parts of the same columns, and are probably also endogenous 

 internuncial fibres. 



Certain cells of the intraspinal system have axis -cylinders 

 that cross with those of the other side, through the dorsal white 

 commissure. 



(/) In addition to the cells which are the trophic centres for 

 the fibres of the ventral roots and the white matter, the grey 

 matter of the cord also contains numerous fibres, which traverse 

 it in every direction, forming a close plexus. Many of these are 

 collaterals of the long and short paths of the white matter. The 

 observations of Sherrington and of G. Mingazzini show that some 



A B 



Km. 178. Section through A, cervical, B, lumbar cord, to show approximate limits of the respective 

 systems of the spinal cord, as shown by embryological research, and principally from prepara- 

 tions of secondary degeneration in one or other of the systems. (Edinger.) la, pyramidal 

 tract of lateral column ; 1, pyramidal tract of ventral column ; 2, ground-bundle of ventro- 

 lateral bundle; 3, ventro-lateral cerebellar tract; 4, dorsal cerebello-spinal tract; f), external 

 limiting layer of grey matter ; 0, column of Burdach ; 7, column of Goll ; 8, zone of entry of 

 roots ; 9, ventral area of dorsal columns. 



of them degenerate after ablation of the Eolandic area of the 

 cerebral cortex, as a result of degeneration of the pyramidal tracts. 



Schiff assumed long conducting tracts for sensations of pain 

 in the grey matter ; but nowadays only short paths are recognised 

 in it. Painful impulses may traverse the fibres of the grey 

 matter, but they emerge after a short course and run up the 

 lateral columns of the opposite side, probably in the region of the 

 tract of Gowers. 



III. From the standpoint of general physiology the spinal 

 cord may be regarded as a highly complex organ or, better, a 

 series of intimately connected segmental organs which receives 

 all the excitatory impulses arising at the periphery, except from 

 the head, by centripetal paths, and reflects them directly by 

 centrifugal paths, or else conducts them farther to the central 

 stations of a higher order, situated in different regions of the 

 brain. Nearly all spinal acts, strictly so-called, present under 



