CHAPTER IV. 

 THE ORGANS OF MOVEMENT : MUSCLES AND JOINTS. 



1. Articulations. Wherever two bones meet in the body 

 an articulation is formed. In some articulations the bones 

 are fixed immovably together, as in the sutures of the skull, 

 (p. 18); in others, to enable us to move, the ends of the 

 bones are so shaped and so fastened together that one 

 can slide over the other. Articulations of this kind are 

 called joints. Joints may be compared to hinges between 

 bones: examples are found between the lower jaw-bone 

 and the rest of the skull; at shoulder, elbow, wrist, hip, 

 knee, ankle; and between the bones of the fingers and toes. 



2. The Movements of the Body are brought about by 

 soft red organs named muscles. The lean of meat is mus- 

 cle, so every one knows what dead muscle is like. Living 

 muscle has the power of shortening, or contracting, with 

 great force. When a muscle contracts it pulls its ends 

 together and swells out in the middle; in other words, 

 // becomes shorter and thicker. If you watch the front of 

 your forearm while you forcibly bend your wrist, you 

 can observe, through the skin, the muscles becoming 

 shorter and thicker. Nearly always the two ends of a 



1. What is an articulation ? Of what kind of articulation are the 

 sutures of the skull examples ? What is a joint? Name some joints, 



2. What is the use of muscles ? What is dead muscle like ? What 

 power has living muscle ? How does it change its shape in contract- 

 ing ? Illustrate. To what are the ends of a muscle usually fixed? 

 What results when a muscle contracts ? 



