370 



THE HUMAN MACHINE 



1 



muscles attached to the bones in such a way that when 



they lengthen or shorten, they raise or lower the bones, 



; thus causing movement. Thus long 



bones act as levers, and allow us to 



move. 



Muscles are always found in pairs, so 

 when one gets longer, the other contracts, 

 thus causing movement. Find two such 

 muscles in your own arm. Muscles are 

 attached to the bones by strong cordlike 

 tendons which are not so elastic as the 

 muscles, but which serve to fasten the 

 muscles firmly to the bones. .Look at 

 the leg bones of a dog or cat skeleton 

 and you will find roughened places in the 

 surface. These are where the tendons are 

 attached. Now you can see what hap- 

 pens when you 

 "pull a tendon" 

 and why it is that 

 you have to be inac- 

 tive for so long after 

 such an accident. 

 Ligaments and Bones. If you 

 have ever tried to carve a duck, 

 you may remember what a hard 

 time you had disjointing the leg 

 bones. As you cut into the joints, 

 you found there white, glistening 

 cords which held the bones to- 

 gether. These are the ligaments, 



T /. , , u . . , i Notice how the tendons are 



and are found between all jointed attached to the muscles and 



bones. When we tear Or injure a are held near to the wrist 



ligament, we have a "sprain." 5^* JSlL2 

 Sprains are often more serious above. 



In what part of the 

 skeleton do you 

 think this fracture 

 took place? Give 

 your reasons after 

 studying the cut on 

 page 369. 



muscle/ 



cement- 



tendon 

 .tewdon. 



