FUNCTIONS OF THE ROOTS OF THE SPINAL NERVES. 259 



upper end of the urostyle. Turn back the flaps of skin, and carry 

 the incision down to the spines of the vertebrse. With a scraper 

 or blunt knife remove the muscles along each side of the vertebral 

 column, so as to lay bare the arches of the vertebrae. With a 

 blunt-pointed pair of scissors, or two saw blades parallel to each 

 other and fitted at a suitable distance into a handle, as devised by 

 Ludwig, cut through the arches of the eighth or last vertebra, 

 taking care not to injure the nerves within the spinal canal. 

 Remove successively from below upwards the seventh, sixth, 

 and fifth vertebral arches, when the tenth, ninth, and eighth 

 spinal nerve roots will come into view. The posterior roots are 

 larger, come first into view, and cover the anterior. The roots 

 may be separated by a seeker. Select the largest posterior root 

 the ninth and with an aneurism needle carefully place a 

 fine silk thread (say a red one) under it. 



(a.) Tighten the ligature near the cord, and observe move- 

 ment in some part of the body. Divide the nerve between 

 the cord and the ligature, and observe further movements on 

 division. 



(6.) With the thread gently lift up the peripheral or distal 

 end of the nerve root, place it on well-protected electrodes, 

 and stimulate it with an interrupted current. No move- 

 ment is observed in the muscles of the limb. 



(c.) Select the posterior root of the eighth nerve, ligature 

 it at some distance from the cord, and divide it on the distal 

 side of the ligature. There is neither contraction of the 

 muscles of the leg nor movement of the body. Place the 

 central stump i.e., the part still connected with the cord on 

 the electrodes, and stimulate it, when movements will take 

 place in several parts of the body. 



(d.) Divide the posterior roots of the seventh and tenth 

 nerves. Observe that the whole limb on that side has be- 

 come insensible. Turn aside the roots of the divided nerves, 

 and expose the anterior roots, which are very thin and 

 slender. Repeat the preceding experiments on the anterior 

 root of the ninth nerve i.e., place a ligature around it, 

 tighten the ligature, and divide the nerve between the cord 

 and the ligature. Stimulate the distal end with an inter- 

 rupted current; this causes contraction of the muscles of 

 the limb supplied by this root. 



