iv PRACTICAL DIRECTIONS 65 



which obscure the view. Notice the belly, and the tendons 

 of origin and insertion (p. 60). Sketch. 



Bend the foot upon the shank as in the ordinary sitting 

 position of the frog. Hold the thigh firmly with one hand, 

 and with the other take hold of the gastrocnemius and pull it 

 upwards or towards the thigh. Note the result. 



3. In a quite freshly killed frog (see p. 31) expose the 

 gastrocnemius as directed above, and with the small 

 forceps give a sharp pinch to the belly of the muscle. Note 

 the contraction following the stimulus. 



Then remove the skin on the dorsal side of the thigh, and 

 separate the muscles in this region so as to expose the sciatic 

 nerve (Figs. 17 and 51). Trace this towards the shank and 

 notice its branch going to the gastrocnemius. Carefully 

 separate the nerve as it traverses the thigh and pinch it with 

 the forceps, noting again the contraction following the 

 stimulus. 



PRACT ZOOL. 



