THE NERVOUS SYSTEM 1327 



these, being displaced inwards into the tract of Goll, terminate in 

 connection with the cells of the nucleus gracilis. 



The tract of Lissauer, or posterior marginal bundle, is close to the 

 outer surface of the cord. It embraces the contiguous parts of the 

 posterior and lateral colimms, and occupies the region of the dorso- 

 lateral sulcus w^here the funiculi of the dorsal nerve-roots enter the 

 cord. It lies between the substantia gelatinosa of Rolando and 

 the surface of the cord. Its fibres are derived from the dorsal 

 nerve-roots, and they ascend close to the substantia gelatinosa of 

 Rolando, in which they terminate at different levels. 



Deseending Tract. — ^The comma tract of Scholtz is situated in 

 the outer part of the tract of Burdach. Its fibres are usually 

 regarded as being derived from the descending branches of the 

 fibres of the dorsal ner\'e-roots, in which case they are exogenous. 

 The other view, however, is that the fibres are intrinsic or endo- 

 genous, 8ind spring from the cells of the dorsal comu of grey 

 matter. 



AssoeiatiOD Fibres. — These fibres are also known as intrinsic, commissural, 

 or intersegmental fibres. Unlike those just described, they are not derived 

 from the dorsal nerve-roots, but spring from the cells of the dorsal comu of 

 grey matter. They are therefore intrinsic or endogenous. Thereafter they 

 enter the white matter of the posterior column and divide into ascending and 

 descending branches. Subsequently these branches re-enter the grey matter 

 of the dorsal comu at different levels, and terminate in connection with its 

 cells. They serve to connect different segments of the cord, and they form 

 ascending and descending bundles. 



The aseendlng bundle lies in the deep or ventral part of the posterior column, 

 close to the dorsal or grey commissure and dorsal median fissure. 



The descending intrlnsie fibres are disposed in two bundles. One is known 

 as the comn-commissural bundle. It is met with in the lumbo-sacral region, 

 and is contiguous to the dorsal comu of grey matter and the dorsal or grey 

 commissure. 



The other descending bundle occupies different positions in the cord at 

 different levels, (i) In the sacral region it occupies a small triangular area 

 in the postero-intemal part of Goll's column. (2) In the lumbar region it 

 Ues contiguous to the centre of the dorsal median fissure and at the corre- 

 sponding part of the dorsal surface of the cord. This bundle is known as the 

 septo-marginal or oval bundle. (3) In the thoracic and cervical regions it 

 may be represented by the comma ttaet of Sehultz, if the fibres of that tract 

 are to be regarded as intrinsic. 



Antero-Lateral Column. — ^The tracts of this column are arranged 

 into descending and ascending, and are as follows: 



Deseending Tracts. Ascending Tracts. 



Crossed Pyramidal Tract Dorsal Spino-cerebellar Tract. 



Direct Pyramidal Tract, Ventral Spino-cerebellar Tract 



Uncrossed Lateral Pyramidal Tract. Spino-thalamic Tract 



Anterior Marginal or Ground-Bundle. Spino-tectal Tract. 



-^ Prepyramidal or Rubro-spinal Tract. 



1^ Bulbo-spinal Tract 



Descending Tracts.— The crossed or lateral pyramidal tract {jasci- 

 culus ccrebro-spinalis lateralis Bj is a long descending tract, of large 

 size, which is situated deeply in the dorsal part of the lateral 



