SUMMARY-. OF THE SPIXAL CORD. 297 



The anatomical points bearing upon the physiological 

 action of the cord are the following : 



The fibres from the anterior roots penetrate the anterior 

 gray cornua directly and are in immediate connection with 

 the prolongations of the motor cells. The motor cells also 

 have prolongations which pass to the brain in the white sub- 

 stance. The motor fibres are thus directly connected with 

 the cellular elements of the cord, the elements probably con- 

 cerned in reflex movements, and the cells are in connection 

 with conducting fibres to the brain. 



The fibres from the posterior roots take several directions. 

 Some of them pass to the gray substance. A portion passes 

 to the posterior columns, some extending upward and others 

 downward. The decussation, which is rendered certain by 

 physiological experiments, has not been satisfactorily fol- 

 lowed by anatomists. It undoubtedly takes place in the gray 

 substance, probably in part by a crossing of the fibres them- 

 selves, and in part by a crossing of prolongations from the 

 cells with which certain fibres from the posterior roots are 

 connected. 



