THE HUMAN BODY AS A MACHINE 219 



3. How do the ankle and the foot of man differ from those 

 of the frog ? 



4. What advantage in the hind legs of a frog being so near 

 the hind end of the body ? 



Conclusion. What adaptions for locomotion found in the 

 frog not found in man ? 



b. A Typical Muscle and its Functions 

 Material. Hind legs of a frog preserved in 4 % formalin. 



1. FROG 



Method. Strip off the skin of the hind leg. 

 Observations. 1. Note the whitish muscle that forms the 

 calf. Is it in a solid mass or in bundles ? 



2. Where is it widest ? The wide part is called the belly. 



3. Look carefully for the endings. Where are they fas- 

 tened ? The glistening white part which attaches a muscle 

 to a bone is called a tendon. 



4. Pull the large muscle in the calf. What movements 

 result ? 



5. How are the muscles related to one another ? 

 Conclusions. 1. What results when a muscle contracts? 



2. Should both muscles of a pair contract at once ? If so, 

 what would happen ? 



3. Why is it necessary that muscles be arranged in pairs ? 



4. What is the advantage of a tendon ? 



2. THE HUMAN BODY 



Method. Grasp the upper right arm with the left hand. 

 Raise and lower the forearm a number of times. Find the 

 muscles that form the pair for moving the forearm. 



Observations. 1. Which one is the larger ? Why ? 



2. What changes take place in the muscles of the arm as 

 they are used ? 



Conclusions. 1. What happens to a muscle when it shortens ? 



2. W T hat happens to bones when muscles shorten ? 



