170 THE STEUCTUKE OF THE HOUSE. 



sessing the property of contracting in length (with 

 corresponding dilatation in width) on the application 

 of a stimulus, usually conveyed to it through the 

 nerve the terminal fibers of which are distributed 

 through it. The electric current, or mechanical irri- 

 tation, will act as a stimulus to contraction, but in 

 the living state the will of the animal, conveyed from 

 the brain along the nerve to the muscle, is the usual 

 cause of action. If the nerve is divided anywhere in 

 its course between the brain and the muscle, the lat- 

 ter will no longer act in obedience to the will, and is 

 said to be paralyzed, although it does not really lose 

 its power of contraction, as may be proved by the 

 application of any other appropriate stimulus either 

 directly to the muscle or to the lower part of the di- 

 vided nerve. 



In order that muscles by their contraction may 

 produce movements, they must be fixed by their two 

 extremities to two different bones, which are con- 

 nected to each other by a movable joint. When the 

 contraction brings the ends of the muscle nearer to- 

 gether than they were before the bones must follow, 

 and their position in relation to one another must be 

 changed. It usually happens that one attachment 

 of a muscle is to a point more fixed than the other, 

 and this is then spoken of as its " origin " ; the at- 

 tachment to the bone that is most movable being 



