CHAPTER III 



THE articulated arm of a skeleton (the arm can be bought 

 separately) should be examined to realise how movements are 

 brought about by muscles. Articulated bones, various useful 

 models of organs and so on, can be obtained from Deyrolle of 

 Paris. 



Attach a cord in the place, say, of the biceps muscle, at one end 

 to one of the bones of the fore-arm near the elbow, at the other 

 end to the bone of the scapula (shoulder-blade) just above the 

 shoulder joint By looping up the cord so as to shorten it the 

 elbow is flexed. If the cord is attached at one end to the ulna 

 where it forms the prominence of the elbow, at the other to the 

 bone of the upper arm, it extends the elbow joint or straightens 

 out the arm, since it is attached on the opposite side of the fulcrum 

 to that of the biceps. It represents the triceps. 



The "Contraction" of Muscle. Take a pithed or beheaded 

 frog, cut across above the pelvic girdle with strong scissors. 

 Remove the remains of the viscera in the posterior part. Seize 

 the skin at the cut edge with forceps and the pelvic girdle with the 

 left thumb and forefinger. The skin can now be pulled off, turning 

 inside out in the process. The muscles of the legs are exposed, 

 and, by the application of electrodes connected to an induction 

 apparatus to each in turn, its action can be observed. 



Tension in Muscle. The string or thread used for the experi- 

 ment described in the text must not be too strong,otherwise sufficient 

 weight required to break it may not be available. 



Spring. Suitable springs may be bought at the ironmonger's. 

 Those of about i in. diameter and 4 or 5 in. long do well. But 

 the exact size is immaterial. 



Nerve-Muscle Preparation. Skin the legs of a pithed frog as 

 above. Prepare the sciatic nerve as on p. 199, but dissecting it free 

 down to the knee-joint. Pass a thread under the tendon of the calf 

 muscle where it is attached to the heel. Tie and divide the tendon 

 below the knot. Separate the muscles from the leg-bone up to the 

 knee. Cut across the thigh-bone at the middle, and remove the 

 muscles attached to the lower part, taking care not to injure the 

 nerve. Finally cut across the leg-bone just below the knee. 



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