THE SPINAL CORD 



227 



(3) Conduction of impulses from the peripheral centripetal 

 nerves through the cells of the 

 gray matter of the cord to the 

 peripheral motor nerves reflexes. 



1. THE MOTOR TRACTS 



These are formed from fibres of 

 both pyramidal columns, the cells of 

 the anterior horns and the anterior 

 roots. 



The pyramidal column descend- 

 ing from the brain gives off, at vari- 

 ous heights, fibres into the gray 

 substance, hence the cross-section 

 of this column decreases as it pro- 

 ceeds downward. The end-tufts of 

 the pyramid fibres come into con- 

 tact with the cells of the anterior 

 horns, those of the crossed pyram- 

 idal tract are in contact with cells 

 on the same side, while those of the 

 direct pyramidal tract are in contact 

 with cells on the opposite side. 

 The fibres of the direct pyramidal 

 tract cross in the anterior white 



commissure just before their ending- ,-, 



& FIG. 19. CROSS-SECTION OF 

 at the cells. THE SPINAL CORD AT VA- 



The axis-cylinders proceed into S&JSZ&SSfc 



the anterior roots from the cells of THE WHITE MATTER. 

 the anterior horn. (Aft " Flech f8' ) 



' . 1, at sixth cervical nerve; II, 



rathological evidence shows that at third dorsal nerve; III, at 



the paths just described are motor. S.h'ZL, "n^e; /v', 

 There are diseases in which the fourth lumbar nerve, pv, direct 

 motor nerves only are paralyzed, %%* ?k&5! 

 and in these cases the pyramidal Cellar tract; # Coil's column, 

 columns and the cells of the anterior horns undergo 



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