CHAPTER IV. 

 THE MUSCLES AND THE BONES. 



Skeletal Muscles. When we look at the skinned car- 

 cass of an animal in the market, we observe that the mus- 

 cles almost completely cover the bones. Those which are 

 attached to the bones are called skeletal muscles. They 

 act upon them as levers, making the motion strong, quick, 

 and accurate. Without bones our motions would be like 

 those of an earthworm or slug, slow and uncertain. The 

 muscles, acting through the bones, can lift a weight that 

 would crush the muscles if laid directly upon them, while 

 a bone, able to support a heavy weight without being 

 crushed, has no power in itself. The muscles have active 

 strength, the bones \wxspassive strength. 



Relation of the Muscles and the Bones. Examine Figs. 

 10, 1 6, and 17. For this work you should have the bones of 

 an arm. Locate the biceps muscle in its relations to these 

 bones as shown in the figures. Feel the biceps of your 

 arm. Note that its thickest part is opposite the most 

 slender part of the bone. But at the enlarged end of the 

 bone the muscle has narrowed to a slender tendon which 

 passes over the joint to be attached to the next bone, thus 

 giving more slenderness, flexibility, and freedom of motion 

 to the joint. Most of the skeletal muscles are attached to 

 bones. There are some exceptions, such as the circular 

 muscle which closes the mouth when the lips are pursed up. 



X-Rays and their Use. By means of X-ray apparatus 



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