90 Practical Zoology. 



The Action of a Frog's Muscle. Kill a frog thus : Into a fruit 

 jar of water put a teaspoonful of ether ; immerse the frog in it and 

 cap the jar. As soon as the frog is motionless cut off its head and 

 run a wire down the cavity of the spinal column, to destroy the 

 spinal cord. Cut through the skin around the base of one of the 

 thighs, and strip off the skin from the whole of the limb. Note 

 that the muscles are of a pale color. The muscles of a frog's 

 thigh are nearly the same in number and arrangement as in man. 

 Examine more thoroughly the calf muscle ; the end by which it is 

 attached below is its insertion, and the upper attachment is its 

 origin. The white cord in which it ends is its tendon. This ten- 

 don is often called the " heel cord," or Achilles' tendon. 



Sever the limb from the body at the hip joint. Separate the 

 muscles along the outer back part of the thigh, and find the white, 

 threadlike sciatic nerve. The nerve must be handled with great 

 care ; it must not be pinched or dragged. Carefully separate it 

 from the surrounding muscles, and turn it down upon the calf 

 muscle. Cut away all the muscles of the thigh, being careful not 

 to touch the nerve where it runs down by the knee. Sever the 

 heel cord below the heel, and separate the calf muscle from the 

 rest of the leg, leaving undisturbed its attachment above ; just 

 below the knee cut away the shin bone, with all the muscles of the 

 leg except the calf muscle. 



There should now remain the thigh bone, with the sciatic nerve 

 running to the calf muscle suspended below. Fasten the thigh 

 bone to some support, such as a clamp on a retort stand. Attach 

 a small hook to the tendon, and suspend from it a slight weight, 

 such as a small key. 



Such a preparation is called a nerve-muscle preparation. It 

 should frequently be moistened with a .7 per cent solution of 

 common salt in water, called normal saline solution. 



Now take a sharp pair of scissors, and snip off the shortest possi- 

 ble portion of the upper end of the sciatic nerve. If the muscle 

 is closely watched at the time when the nerve is cut, it will be 

 seen to thicken and shorten, and to lift the weight. If the muscle 



