BONES AND MUSCLES 



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mine how these muscles are attached to the bones? At how many- 

 points are they attached? 



Explain how movement of the leg results from contraction (shorten- 

 ing) of certain of the muscles. What must occur when some of the 

 muscles contract ? (Look at the position of the muscle on the opposite 

 side of the leg.) 



Note the shape of your upper arm. To what is the rounded surface 

 due? Move it and watch what happens to the muscles. Now 

 examine the skeleton or a diagram to see if you can make out just 

 where the muscles are attached. Why do muscles cause movement? 

 Explain fully. What use, other than movement, have muscles ? 



Practical Exercise 2. From a study of diagrams and skeletons of a man 

 and of some other mammal, as a cat or a dog, make labeled diagrams for your 

 workbook to show the position of the main parts of the skeleton, vertebral 

 column, skull, shoulder and pelvic girdles, and the appendages. 



Bones and muscles. The body is built around a framework of 

 bones. These bones, which are bound together by tough ligaments, 

 fall naturally into two great groups : 

 the bones of the trunk and head, 

 namely, the vertebral column, ribs, 

 breast bone, and skull, which form 

 the axial (ak'si-al) skeleton; and 

 the bones of the appendages (the 

 framework of the arms and legs), 

 which, together with the bones at- 

 taching them to the axial skeleton, 

 form the appendicular (ap-en-dik'ti- 

 ldr) skeleton. 



To the bones are attached the 

 muscles of the body. Movement 

 is accomplished by the contraction 

 of muscles, which are attached so 

 as to cause the bones to act as 

 levers. Muscles usually act in 

 pairs : one muscle extends while the 

 other flexes or bends. Bones also 

 protect the nervous system and 

 other delicate organs. The bony cranium (kra'ni-#m), inclosing 

 the brain, is an example of such protection. The internal skeleton 

 also gives form and rigidity to the body. 



•skccll 



.clavicle 

 sternum 



..Taumems 



-vertebra 



.ulna 



.racCiurs 



What are the uses of the skeleton ? 



