120 



HUMAN PHYSIOLOGY. 

 FIG. 32. 



DIAGRAM SHOWING THE COURSE, THROUGH THE SPINAL CORD, OF THE MOTOR AND 

 SENSORY NERVE FIBRES. 



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

 fibres take their origin, and in which the sensory fibres terminate. The motor tract 

 from the right side l passes down through the crus, through the pons to the medulla 

 oblongata, where it divides into two portions : ist, 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 fibres at different levels, which pass into the gray matter 

 and become connected with the muscles, M, through the multipolar cells ; 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 fibres 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. 



