WHITE MATTER OF THE SPINAL CORD. 



1039 



Based on the collective evidence contributed by these methods anatomical, 

 physiological, and developmental it is possible to locate and trace with fair accuracy 

 a number of fibre- tracts in the cerebro-spinal axis. Since they are undergoing 

 continual augmentation or decrease, their actual area and position are subject to 

 variation, so that the detailed relations in one region of the cord differ from those 

 at other levels. The accompanying schematic figure, therefore, must be regarded 

 as showing only the general relations of the most important paths of the cord, 

 and not as accurately representing the actual form and size of the fibre-tracts! 

 It must also be appreciated that the definite limits of these tracts in such diagrammatic 



FIG. 893. 



Association tracts 



Rubro-spinal 



tract 

 Tecto-spinal 



tract 

 Spino-thalamic 



tract 



Spino-olivary 

 tract (Helweg) 



Vestibulo-spinal tract 

 Cerebro-spinal tract' " Sulco-marginal fibres 



Diagram of spinal cord, showing position of chief tracts and relations of their component fibres to nerve-cells; 

 1-5, posterior root-fibres entering root- zone (R.Z.) and Lissauer's tract (L.)- open circles (o) indicate that fibres pass 

 up and down ; e, c, collaterals from long ascending tracts (i, 2) to anterior root-cells; 3, fibres ending around cells 

 of Clarke's column; 6, fibres forming direct cerebellar tract; 7, 8, fibres forming Cowers' tract; 9, 10, fibres from 

 lateral and direct pyramidal tracts; n, n, anterior root-fibres ; V.F., ventral field; O.F., oval field; C.B., comma 

 bundle. 



representations seldom exist in reality, since the fibres of the adjacent paths in 

 most cases overlap, or, indeed, extensively intermingle, so that the fields seen in 

 cross-sections may be shared by strands belonging to different fibre-systems. 



The Fibre-Tracts of the Posterior Column. The subdivision of the 

 posterior column of white matter by the paramedian septum into two general 

 parts has been noted (page 1028). Of these the inner one is the postero-median 

 fasciculus, or tract of Goll (fasciculus gracilis), and the outer one is the postero- 

 lateral fasciculus or tract of Burdach (fasciculus cuneatus). These tracts are 

 so intimately associated with the fibres entering by the posterior roots of the spinal 

 nerves, that the general relations and behavior of these fibres must be considered 

 in order to understand the composition of the posterior columns, as well as that 

 of certain secondary paths. 



All sensory impulses that enter the spinal cord do so by way of the posterior 

 root-fibres. The latter are the centrally directed processes (axones) of the neurones 

 whose cell-bodies lie within the spinal ganglia situated on the dorsal roots of the 

 spinal nerves. They convey to the cord the various impulses collected by the 

 peripherally directed processes (the sensory nerves) from the integument, mucous 

 membranes, muscles, tendons and joints from all parts of the body, with the 

 exception of those served by the cranial nerves. The impulses thus conducted are 

 transformed into the impressions of touch, muscle-sense, heat, cold and pain. 

 The last being probably the result of excessive stimulation that by its intensity 

 causes discomfort in various degrees, the existence of special paths for the conduc- 

 tion of painful impressions is unlikely. It is evident that the larger part of the 



