FIG. 22. DIAGRAM SHOWING THE COURSE, THROUGH THE SPINAL CORD, OF THE 

 MOTOR AND SENSORY NERVE-FIBERS. 



B and B' represent the right and left hemispheres of the brain, from which 

 the motor fibers take their origin, and in which the sensory fibers termi- 

 nate. The motor tract from the right side, i, passes down through the 

 crus, through the pons to the medulla oblongata, where it divides into two 

 portions: (i) The larger portion, ninety-seven per cent., crosses over to 

 the opposite side of the cord and passes down through the lateral column. 

 It gives off fibers at different levels, which pass into the gray matter and 

 become connected with the muscles, M, through the multipolar cells. (2) 

 The smaller portion, three per cent., does not cross over, but descends on 

 the same side of the cord in the anterior column and supplies the 

 muscles, m. The same is true for the motor tract for the left hemisphere. 



The sensory -fibers from the left side of the body enter the gray matter through 

 the posterior roots. They then cross over at once to the opposite side of 

 the cord and ascend to the hemisphere, partly in the gray matter, partly 

 in the posterior column. The same is true for the sensory nerves of 

 the right side of the body. 



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