872 



THE TRACTS OF WHITE MATTER. [BOOK in. 



others as undergoing ascending degeneration. Further, the delimi- 

 tation of tracts of white matter by the process of degeneration 

 agrees so well with the results of the embryological method as to 

 leave no doubt that the white matter does consist of tracts which 

 differ from each other in nature and in function. 



The several tracts thus indicated vary in different regions 

 of the cord. They may be broadly described as follows. 



I. Descending tracts, that is to say, tracts which undergo a 

 descending degeneration in the sense noted above. 



The most important and conspicuous is a large tract (Fig. 100, 

 cr. P.) occupying the posterior part of the lateral column, coming 



UM^ 



ac.a.l. 



FIG. 100. DIAGRAM TO ILLUSTRATE THE GENERAL ARRANGEMENT or THE SEVERAL 

 TRACTS OF WHITE MATTER IN THE SPINAL CORD. (Sherrington.) 



The section is taken at the level of the fifth cervical nerve. The relations of 

 the tracts in different regions of the cord are shewn in Fig. 104. 



The ascending tracts, tracts of ascending degeneration, are shaded with dots, 

 the descending tracts, tracts of descending degeneration, are shaded with lines; 

 the shading is in each case put on one side of the cord only, the reference letters 

 being placed on the other side. 



cr.P. crossed pyramidal tract, or more shortly pyramidal tract. d.P. direct 

 pyramidal tract, shaded on the side opposite to that on which cr.P. is shaded, 

 in order to indicate the difference of the two as to crossing. C.b. cerebellar 

 tract, s.lr. and c.r. together indicate the median posterior tract or 'tract of 

 fibres of the posterior roots, c.r. representing, as is explained more fully in the 

 text, the cervical and s.lr. the sacral, lumbar and dorsal roots, asc.a.l. the 

 antero-lateral ascending tract, desc.l. the antero-lateral descending tract. 

 The area, not shaded, marked x, is the small descending tract or rather patch 

 mentioned in the text as observed, in certain regions of the cord, in the 

 external posterior column rz. The small area at the tip of the posterior horn, 

 marked L, is the posterior marginal zone or Lissauer's zone. 



close upon the outer margin of the posterior horn, and for the 

 most part not reaching the surface of the cord. We shall have 

 to return to this tract more than once, and may here simply say 

 that it is most distinctly marked out by both the embryological 

 and the degeneration methods, that it may be traced along the 

 whole length of the cord from the top of the cervical region to 

 the end of the sacral region, and that it enters the cord from 



