110 LABORATORY EXERCISES 



Let the bone cool; then examine it. Is the burnt bone tough, 

 or brittle? What did the burning remove from it? 



EXERCISE 100 

 MUSCLES AND TENDONS 



Apparatus and Materials. Pocket knife or dissecting needle (see 

 Exercise 99); tough, lean beef and tender beef; tendon from a sheep's 

 hoof, a heavy book, magnifying glass (?). 



a. Read 355 and 356 of the text. Ask the butcher for 

 a small piece of lean beef that is sure to be tough. From, what 

 part of the animal does it come? Ask also for a small piece 

 of tender beef. Cut across the muscle fibers of each, and ex- 

 amine the cut ends. Is there any difference in their appear- 

 ance? Use a magnifying glass if possible. 



Cook the tough piece until the fibers can be picked apart 

 (not cut) with a knife or needle. What is the name of the 

 tissue between them? Why was the piece tough? 



6. Recall the appearance of the tendon in the chicken's foot 

 (Exercise 98). Ask the butcher to get for you the tendon in 

 the hoof of a sheep; describe it. 



c. Place one forearm on the table, with the elbow on the table 

 and the palm upward. Let the arm and hand be relaxed (limp) . 

 With the other hand find the tendon that attaches the biceps 

 muscle to the radius of the lower arm (see Fig. 277 of text) . Note 

 how it stiffens when you raise the forearm, especially if you 

 have a considerable weight, such as a heavy book, in your hand. 



d. Repeat c, but feel of the biceps muscle in your upper arm 

 instead of the tendon. How does it change? 



e. To what class of levers does the forearm belong? See 

 Fig. 277. Would you need to exert more, or less, force to lift 

 a flatiron that is in your hand than if it were attached just 

 above your wrist? Why? 



