30 



PHYSIOLOGY FOB THE LABORATORY 



bands. The model consists of three pieces of wood ; the 

 longest represents the humerus, the smallest represents 

 together the radius and the ulna, and the broadest repre- 

 sents the shoulder-bone, or scapula. A rubber band 



FIG. 2. A model of an arm. 



attached at a below the elbow-joint and at b above the 

 shoulder-joint represents the biceps muscle. The rubber 

 band attached at e and / represents the triceps muscle. 



1. Adjust the three bands so that the arm hangs down 



straight. Show how the muscles work in opposi- 

 tion to each other over the joints. How is the 

 joint made rigid? 



2. Unfasten the band at e and/. What happens to the 



arm ? What muscle causes this motion ? 



3. Replace the rubber band ef and unfasten the band cd. 



What happens to the arm ? What muscle does the 

 work? 



4. If both ef and cd are unhooked, what is the position 



of the arm ? What muscle causes this motion ? 



5. Remove the piece of wood representing the scapula, 



and readjust the muscles to represent the move- 

 ments of the foot. 



