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Prof. C. S. Sherrington and Dr. E. E. Laslett. [Nov. 5, 



examined, we find there may be distinguished two sets. For physio- 

 logical description it is in some ways convenient to regard the length 

 of the spinal cord as divisible into regions ; thus, a brachial for the 

 fore limb, a thoracic for the trunk, a crural for the hind limb, a pelvic 

 for pelvic organs, a caudal for the tail, and so on. A reflex initiated 

 via an afferent path of one such spinal region may evoke its peripheral 

 effect by efferent paths of a spinal region other than that to which the 

 original entrant path belongs. Such a reflex has in a former paper by 

 one of us* been termed a " long " spinal reflex, in contradistinction 

 to reflexes whose centripetal and centrifugal paths both belong to 

 one and the same spinal region. The latter reflex it was proposed to 

 term " short."! Analogously, in the aborally-running fibre-systems of 

 the spinal segments examined, by our experiments fibres of two cate- 

 gories are found, one a set passing beyond the limits of the spinal 

 region in which they arise, the other not passing beyond those limits. 

 The former we would term "long spinal," the latter "short spinal" 

 fibres. In each of these main categories there can be distinguished 

 fibres of various intermediate length. 



Again, the fibres of each of the above two categories may be clas- 

 sified into two sets or tracts, according to their topography relatively 

 to the cross-section of the cord. Fibres of both of the above categories 

 are situate both in the lateral columns and in the ventral columns of 

 the cord. It is useful, at least for descriptive purposes, to indicate 

 this by terminology. We thus recognise in the aborally-running 

 intrinsic spinal fibre systems the following sets or tracts : (a) Ventral 

 shart fibres, (/3) ventral long fibres, (y) lateral sliovt fibres, (8) lateral long 

 fibres. It must be added that the distinction into lateral and ventral 

 is somewhat artificial, as there exists often, especially in the case of the 

 " short " fibres, no distinct gap between the ventral and lateral fields of 

 distribution of the fibres in the transverse area of the cord. 



In regard to the " long " fibres, we find that in all the regions 

 examined by our experiments there is no evidence of decussation of 

 these tracts. This statement does not exclude the possibility that the 

 collaterals or the fine ultimate terminals of these fibres may in some 

 cases penetrate in the grey matter across to synapses in the crossed 

 side of the grey matter. We have at present no reliable microscoiDical 

 evidence for or against such a possibility. But all our evidence is 

 consentient that the fibres themselves do not pass from the white 

 columns of one side of the cord into those of the crossed side, that is, 

 do not in the ordinary sense decussate. 



A similar statement seems also to hold true for the "short " fibres, 

 thus confirming Munzer:| it is certainly true of the majority of the 



* C. S. Sherrington, ' : Croonian Lecture," 'Phil. Trans.,' 1897. 

 f Ibid. 



X ' Prager Medic. Wochenschr.' 1895. 



