THE NERVOUS SYSTEM 



469 



III. The Dorsal Spino-cerebellar Tract {Tract of Flechsig, 

 Direct or Uncrossed Cerebellar Tract). — This tract lies along the 

 dorsal-lateral periphery of the cord, being bounded internally by the 

 crossed pyramidal tract (Fig. 319 and Fig. 326). The fibres of the 

 direct cerebellar tract are the axones of the cells of Clarke's column 

 (tautomeric column cells) (Figs. 

 326, 327 and 331). These axones 

 cross the intervening gray matter 

 and white matter of the same 

 side and turn upward as the 

 direct cerebellar tract. In the 

 medulla they form part of the 

 restiform body or inferior cere- 

 bellar peduncle and pass to the 

 cerebellum. • Here they enter the 

 gray matter of the vermis of the 

 same or opposite side, ending in 

 ramifications among the nerve 

 cells. Some fibres either end in, 

 or send off collaterals to, the 

 cerebellar nuclei. The tract first 

 appears in the upper lumbar 

 cord, and increases in size until the 

 upper limit of Clarke's column 

 has been reached (page 456). 



As already noted above, some 

 fibres of the posterior root, or 

 their collaterals, end in the 

 column of Clarke. This path is 

 composed then of two systems of 

 neurones, spinal ganglion cells 

 and Clarke's column cells, and is 

 uncrossed (with the exception 



that some fibres are interrupted in the nucleus lateralis of the 

 medulla and that some of the fibres from the nucleus lateralis 

 cross). (Fig. 345.) 



rv. The Ventral Spino-cerebellar Tract. — This tract lies along the 

 periphery of the cord, extending from the anterior Hmit of the direct 

 cerebellar to about the exit of the ventral roots (Fig. 319 and Fig. 326). 

 It is probably formed by axones whose cell bodies are scattered 



Fig. 327. — Diagram showing Beginnings 

 of Principal Long x\scending Tracts of Cord 

 and Termination of Lateral Pyramidal 

 Tract. Each group of neurones is repre- 

 sented by one or two neurones, d.s-c, 

 Dorsal spino-cerebellar tract; p, lateral 

 pyramidal tract; s-t., spino-thalamic tract; 

 v.s-c, ventral spino-cerebellar tract; v.r., 

 ventral root. 



