TRACTS OF THE SPINAL CORD. 359 



Lesions. The pyramidal tracts (especially the lateral) are 

 involved in lateral sclerosis and in amyotrophic lateral sclerosis; 

 and, as a consequence of it, both voluntary and inhibitor}' impulses 

 from the brain are interfered with, hence the spastic paralysis 

 and exaggerated reflexes. The pyramidal tract may be more 

 or less involved in insular sclerosis and in bulbar paralysis, and 

 the symptoms vary with the amount of sclerosis. Gliosis of the 

 pyramidal, cerebello-spinal and posterior tracts (Dejerine and 

 Letulle) has been demonstrated in Friedreich's hereditary ataxia, 

 and the involvement of the pyramidal tracts explains the spastic 

 paralysis which affects both arms and legs. In ataxic paraplegia 

 (Gowersi) there is diffuse sclerosis of the lateral and posterior 

 columns of the cord. It is the degeneration in the pyramidal 

 tracts that causes the spastic gait, incoordinated arm movements 

 and early increase of the reflexes, observed in that affection. 



The marginal tract (fasciculus marginalis, Lissaueri) is a 

 small tract composed of the ascending branches from the outer 

 set of fibers in the posterior roots of the spinal nerves (Figs. 102 

 and 103). It is situated in the lateral column on the outer surface 

 and apex of the posterior columna. Its fibers are of small caliber 

 and, after ascending a short distance, end about the cell-bodies 

 of the substantia gelatinosa. 



Tracts of the Posterior Column of the Cord (Fig. 101). 

 In the posterior column of the spinal cord, there are, first, two 

 ascending and two descending tracts, derived from posterior 

 nerve roots; second, the posterior fasciculus proprius, which is 

 much scattered and is little understood; and, third, the entry zone 

 occupied by the incoming fibers of the posterior roots. 



Entry Zone (Figs. 102 and 103). Over the apex and along 

 the medial surface of the posterior columna of gray substance the 

 posterior roots of the spinal nerves enter the cord and divide 

 T-like into ascending and descending branches. The name 

 entry zone is well applied to this region. The presence of hori- 

 zontal fibers distinguishes the entry zone from the longitudinal 

 tracts. The root-fibers of small caliber and many collaterals 

 very soon enter the gray substance. The large fibers, in part, 

 enter the dorsal nucleus, but the greater number form the longit- 



