620 PHYSIOLOGY. 



the non-paralyzed member lias, nevertheless, lost its muscular energy ; 

 also why a unilateral cerebral lesion is able to cause permanent con- 

 tracture of the two inferior members or an exaggeration of the re- 

 flexes of the side not paralyzed. 



The vestibulo-spinal tract runs from the vestibular nucleus, 

 which contains Deiters's nucleus, and descends in the antero-lateral 

 columns, arborizing about the anterior horns. This tract is connected 

 with the nucleus fastigii of the cerebellum. 



The deep lateral trac^, lateral mixed tract, or lateral marginal 

 zone, is molded upon the lateral concavity of the gray matter. It 

 incloses at the same time the fibers coming from the anterior motor 

 horns, the gray column of Clarke, and the gray intermedio-lateral 

 column. 



The lateral ground-bundle is continued in the posterior longi- 

 tudinal bundle and ends in the posterior corpora quadrigemina. 

 The posterior longitudinal bundle puts the sensory bulbar nuclei and 

 the tubercula quadrigemina in communication with the nuclei of the 

 motor nerves of the eyes and the motor nerves of the trunk. 



Posterior Columns. The posterior columns comprise that area 

 of the spinal cord lying between the postero-lateral groove and the 

 posterior median groove. It is composed of fine fibers in that por- 

 tion nearest the median groove, and is remarkable for its abundance 

 of neuroglia. 



This large tract is divided into two tracts: one internal, the 

 other external. 



The internal one, or column of Goll, is especially apparent in 

 the upper part of the cord. Here it occurs in the form of a trian- 

 gular pyramid whose base is turned toward the central gray com- 

 missure. It is formed by long commissural fibers which arch so as 

 to unite the posterior horns. It proceeds from the level of one pos- 

 terior horn to that of a higher level. It incloses the posterior root- 

 fibers which compose the major portion of it. The fibers of Goll are 

 very long, ascending from the cauda equina to GolPs or gracilis 

 nucleus of this tract in the medulla. Its trophic centers are in the 

 cells of the ganglion of the posterior root. 



The more external and cuneiform tract, column of Burdacli, con- 

 tains shorty commissural, longitudinal fibers which have the same dis- 

 tribution as those of Goll, and sensory fibers, which also spring from 

 the posterior horns, but do not sojourn there. Almost immediately 

 they pass into the mixed lateral column of the same side, or, travers- 

 ing the commissure, cross into the opposite tract. At the level of 



