19 



Prepare Frog. 



(1) Kill, decapitate, divide, and skin the hind part as iri 

 earlier lesson. (2) Lay the frog on its belly. Raise the 

 urostyle in forceps, holding the lower end and cut up each side. 

 Cut it across at the base, taking care not to cut the nerves beside 

 it. (3) Cut across each iliac bone at the upper part and at 

 lower end (talcing care not to touch nerves seen in front}. (4) Divide 

 the spinal column vertically in the middle line. (5) Divide the 

 pelvis vertically in the middle line (one half to each two students). 

 (6) Dissect out the sciatic nerve from the spinal column to the 

 lower end of the thigh. (7) Now separate the muscle from 

 the tibia with a glass hook and cut through the fascia of 

 the sole of the foot, into which the gastrocnemius muscle is 

 inserted. (8) Cut away all the thigh but the lower end of the 

 femur (fig. 11 (1, 2, and 3)), taking care not to injure the nerve. 



r | 



" 



E"x tensors 



FIG. 11. 



(9) Cut through the tibia below the knee (fig. 11 (4)), and 

 thus remove it and the foot. 



C. Bring the Preparation on to the Apparatus. 



(1) Lay the muscle and nerve upon a piece of blotting 

 paper thoroughly saturated with '75 % NaCl solution and 

 placed on the cork plate of the frogboard. (2) Attach 

 the tendon by a thread and hook or clip to the middle 

 hole of the short limb of the crank lever. (3) Fix the 

 femoral end of the muscle to the cork plate by a pin passed 

 through the femur, so that the lever is supported in a hori- 

 zontal position by the thread (fig. 12). (4) Put a small 

 weight, 5 grms., on the lever just clear of the stand. (5) 

 See that the lever is not resting on the screw-pin below it. 

 (6) Place the nerve upon the electrodes, which may be 



