60 ELEMENTARY PHYSIOLOGY. X. 



7th and 8th, and the 8th and 9th cause some movements 

 in common, and that in general the extensors overcome 

 the flexors. Expose the gastrocnemius, cut the Achilles 

 tendon, pin down the knee and ankle-joints; stimulate 

 again and note that contraction of the muscle is ob- 

 tained from two nerve roots. 



b. On the opposite side, remove the ileo-fibularis 

 muscle. Tie the sciatic in the upper part of the thigh 

 and cut the nerve above the ligature. Hold up the nerve ; 

 it will be seen to divide into two branches, one the 

 peroneal nerve (external popliteal) passing dorsally over 

 the knee, the other the tibial nerve (internal popliteal) 

 passing more ventrally. Tie the peroneal nerve close to 

 its point of branching from the sciatic and cut it just 

 above the ligature. 



Move the leg away from the mid-line, and bend the 

 foot at the ankle-joint. Stimulate the tibial nerve with 

 weak faradic currents for a few seconds. The leg will be 

 drawn to the mid-line, there will be extension at the 

 ankle-joint, the toes will be bent towards the plantar 

 surface, and drawn together. Make a sketch of the 

 position of the limb. 



Stimulate similarly the peroneal nerve. The limb will 

 be straightened at the knee, the foot bent back, and the 

 toes separated widely. Tear off the skin, cut the tendo 

 Achillis and stimulate again; the lower leg will be bent 

 back at the knee and the bending of the ankle will be 

 much greater. 



Note that the gastrocnemius contracts on stimulating 

 the tibial nerve but not on stimulating the peroneal 

 nerve. 



