ACTION OF MUSCLE. 13 



We have now seen the muscles themselves, not covered by 

 skin. Our muscles are very much like those of the rabbit, 

 only larger. But if we would learn more fully the action of 

 muscle, we need to go to another animal, the frog. 



The Action of 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. 



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, thread-like 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 or ring 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. 



