MOTION. 1 5 



of form, but because extra strength and endurance may 

 be needed in case of accident, to save one's own life or that 

 of others. In a case of fire the ability to climb, to go up 

 or down a rope " hand over hand," may be all important. 

 Any one's life may depend on his ability to run far and 

 swiftly, to swim, to jump, or to lift a heavy weight. 



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, giving to motion strength, quickness, 

 and precision. 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 have passive strength. 



Relation of the Muscles and the Bones. Suspend the skeleton 

 from the ceiling in the most open space in the room. Let the pupils 

 study it ; not to learn the names of all the bones, but to get a general 

 idea of the forms and relations of the parts. It is well to have the 

 skeleton constantly at hand, to show the location of the various organs 

 as they are taken up. If possible, supply the class with separate bones 

 from another skeleton, and let the pupils place each separate bone 

 alongside the corresponding one in the complete skeleton. 



Pass to the skeleton, and locate the biceps muscle. After examining 

 Fig. 2, show the points of its origin and insertion. 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. The muscle which closes the mouth, as in 

 pursing up the lips, is not attached to any bone, but in shortening 

 reduces the aperture. 



