108 



HUMAN PHYSIOLOGY. 

 FIG. ii. 



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 * 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 



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. 



