62 THE HOUSE I LIVE IN. 



The arm and hand, taken together, consti- 

 tute a most wonderful apparatus for motion. 

 The particular structure of the joints, as well 

 as the peculiarities of the hand, must be re- 

 served for another place ; but it is necessary to 

 say a little about the arm. 



The bones of the arm have a slight resem- 



O 



blance to those of the leg. The upper part 

 consists of only one bone. This is long and 

 round, and is called the humerus. It is fast- 

 ened above to the scapula. Below, at the 

 elbow, it is connected to the two bones of the 

 lower half of the arm, by a joint like a hinge, 

 and by ligaments or straps, which go from near 

 the end of the upper bone to the end of the 

 others. The largest of the two latter bones is 

 called the ulna, which is a Latin word for 

 cubit, because the arm, below the elbow, is 

 usually considered about a cubit in length. 

 The smaller one is called the radius, or spoke, 

 from its supposed resemblance to the spoke of 

 a wheel. 



The connection at the shoulder is such, that 

 the arm can be moved in almost every con- 

 ceivable direction. The elbow joint only ad- 



