PROBLEM 166 189 



At how many points are they attached? Explain how move- 

 ment of the leg results from contraction (shortening) of certain of 

 the muscles. What must occur when some of the muscles con- 

 tract? (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? 



Conclusion. 1. Why do muscles cause movement? Explain 

 fully. 



2. What use, other than movement, have muscles? 



Problem 166 : To study the structure and uses of the skeleton. 



Materials. Prepared human skeleton, manikin. 



Observations. Note that the skeleton is divided into two 

 groups of bones : a main framework of the body, the axial skeleton ; 

 and a framework for the appendages, the appendicular skeleton. 

 In life the bones are attached to each other by tough ligaments. 

 Why are the bones jointed? Notice the bones of the head, 

 skull, and face. Knowing that the skull covers part of the 

 delicate nervous system, the brain, what would you say its 

 use was? 



Note that the backbone, made up of numerous pieces of bone, 

 has a hole running through it. This hole contains in life the spinal 

 cord. 



Attached to the vertebrae of the backbone are the ribs. Com- 

 pare the position on the manikin. What is one use of the ribs? 

 Feel your own ribs ; bend forward, and take a full breath. What 

 is another function of your ribs? (Remember, to obtain move- 

 ment, muscles must be attached to bones. Why?) 



Notice that the arm is attached to the main skeleton by means 

 of two bones, the collar bone and the shoulder blade. These 

 bones form the pectoral girdle. The leg is in the same way at- 

 tached to a group of strong bones called the pelvic girdle. 



Notice various bones, such as the long arm bone (humerus), 

 shoulder blade, pelvic bones, the spines on the ribs, for roughness 



To THE TEACHER. A demonstration should be shown at this point to illus- 

 trate the structure of striated and plain muscle tissue. Detailed laboratory work 

 on this material is not desirable. 



