06 BONES, JOINTS, MUSCLES. 



themselves, therefore, they pull the arm backwards, 

 or stretch it out. For this reason they are called 

 extensors, or extending muscles. 



Now bend your arm. This motion is perform 

 ed by the muscles on the front of the arm. These 

 are fixed at their upper ends above the elbow, near 

 the shoulder, and at their lower ends just below 

 the elbow. When these contract or shorten them- 

 selves, they pull the arm upwards, and thus bend 

 it. On this account they are called flexors, or bend- 

 ing muscles, and the same throughout the body. 



Muscles, before they terminate, or are fixed into 

 the bone, are generally reduced to a thick cord of 

 white glistening substance, which is very strong, 

 and called tendon. Where this passes over joints, 

 it is bound down by a strong band, to keep it in 

 its place when the muscle is acting, and to preserve 

 the shape or symmetry of the parts. 



The power with which muscles contract is very 

 great, and is termed irritability. Our voluntary 

 muscles are soon tired, and require rest, or they 

 get weak, but those which are involuntary are in 

 perpetual motion, and are never fatigued, but keep 

 acting, without rest, from the hour of our birth to 

 that of our death. 



Questions. 



Of what do bones chiefly consist ? 

 What name is given to all the bones when put together ? 

 How are the bones held together, and what are their ends 

 lined with ? 



