94 PRACTICAL ZOOLOGY. 



apart the muscles, and find the sciatic nerve ; with a 

 sharp pair of scissors (while watching closely the foot) 

 sever this nerve ; what takes place ? 



3. Hang up as before, and pinch the toes of each foot ; 

 what difference is now observed? 



4. With the forceps alternately pinch the two ends of 

 the severed sciatic nerve ; what takes place as these 

 two ends are pinched? 



5. Run a wire down the spinal column, twisting it about 

 to destroy the spinal cord ; what occurs while this is 

 doing ? 



6. Pinch the toes as before; what results? 



7. Again pinch the end of the sciatic nerve, still con- 

 nected with the parts below, being careful to pinch a 

 little lower than before. 



THE FROG'S MUSCLES. 



Make a circular cut through the skin at the top of the 

 thighs, and pull off the skin of the hind limbs like a pair 

 of hose. Notice the pale color of the muscles. The mus- 

 cles of the frog's thigh are nearly the same in number and 

 arrangement as in man. Notice especially the calf-muscle ; 

 the end by which it is attached above, the less movable 

 end, is its origin. The muscle tapers into a strong, white 

 tendon below. The end of the muscle at its more 

 movable end (or its attachment by a tendon at its more 

 movable end) is its insertion. 



Observe the thin, transparent membrane covering the 

 muscle, the muscle-sheath. Tear the muscle to pieces, 

 and note its fibrous structure. Put a bit of the muscle in 

 a drop of water on a slide, and cover with a cover-slip ; 



