8 ORIGINAL ARTICLES 



impossible, as Edinger has pointed out, with one section to 

 cause degeneration in all the fibres constituting that tract, or in 

 the complete length of the fibres constituting the tract. 



With regard to their function, I feel it necessary to raise a 

 note of warning with regard to the loose employment of the term 

 " descending tracts," or " descending fibres," which is so frequent 

 in text-books and in conversation. It, of course, by no means 

 follows that because a tract undergoes secondary degeneration 

 downwards that therefore it conveys nervous impulse downwards. 

 A good illustration of this is the fact that if a posterior root be 

 cut on the peripheral side of its spinal ganglion, the fibres 

 degenerate towards the periphery (the ordinary Wallerian law), 

 whereas, of course, it is well known that these same fibres must 

 convey nervous impulses in exactly the opposite direction. 

 Therefore, although the fibres described above by various 

 observers, and the set of fibres to which I have called attention 

 in the present paper, degenerate downwards, it by no means 

 follows that they convey impulses downwards. There is a 

 strong presumption that they do convey impulses downwards, 

 but there is no actual proof at present. It may be that they 

 serve to couple up movements of the eyes, or movements which 

 have their centres in the mid-brain, with movements of the hand 

 and lower portions of the body. It may be, also, that they are 

 merely long and short associational fibres subserving in some 

 instances co-ordination, or, of course, their function may be a 

 mixture of the two. Also, van G-ehuchten has suggested that they 

 may serve to innervate the lower organic functions. Further 

 work on this point is much needed. 



CONCLUSIONS. 



From the above considerations it follows that apart from the 

 bundle of fibres which under certain circumstances undergo 

 secondary descending degeneration in the posterior columns of 

 the spinal cord as described by many observers, viz. : (1) a set 

 of fibres in the postero-external columns occupying the comma 

 tract area and the immediate vicinity of the inner margin of the 

 posterior horns ; and (2) fibres lying more mesially in proximity 

 to the postero-median septum there is also, as shown in the 

 accompanying photographs of the monkey's spinal cord, a well- 



