SPINAL CORD. 107 



(6) Posterior nerve-roots enter into the posterior horn of the 

 gray matter, and the fibres break up to form Gerlach's network, 

 communicating with the large multipolar cells, but some fibres 



FIG. 29. 



Transverse Section of the Spinal Cord in Man (lumbar region). 



cross through the gray commissure to the opposite side. The fibres 

 of the posterior roots are afferent or sensory fibres. 



If the anterior nerve-roots be cut, what is the result ? 



The anterior nerve-roots are efferent or motor ; therefore their 

 division results in complete loss of motion in the parts supplied. 

 If the distal portion of the cut nerve-root be stimulated, muscular 

 action follows, while irritation of the proximal portion produces no 

 noticeable effect. 



What follows division of the posterior roots ? 



Loss of sensation without loss of motion. Stimulation of the 

 distal portion of the cut posterior root produces no result, either 

 in sensation or motion. Irritation of the proximal end will, how- 

 ever, cause very acute pain. 



Is the course of the fibres through the spinal cord known ? 

 No, not fully. Certain fibres have been traced with fair accu- 



