10 PHYSIOLOGY AND TEMPERANCE. 



they have of contracting and relaxing, produce motion of the 

 joints. They act upon the principle of the levers one or 

 other of the three kinds. In the attachment of the muscles 

 we see the admirable purpose which the various prominences 

 and depressions upon the bones are intended to serve. 



4. Fascia. The muscles are invested and bound down by 

 a fine, thin membrane, called fascia, which protects and keeps 

 them in place. 



5. The Nerves. The muscles are moved and controlled 

 through the nerves supplied to them. The nerves form the 

 connecting links between the muscles at one end and the 

 brain and spinal cord, or marrow, at the other. The brain 

 and spinal cord may be called the headquarters of the nervous 

 system. Nerve cords of various sizes extend from the head- 

 quarters to the numerous muscles of the body, where they 

 divide and ramify. Each nerve is like a telegraph wire, along 

 which are conveyed communications from the nerve centres 

 to every part of the muscular system. Orders may be trans- 

 mitted from the brain to a muscle, when it is to move, how it 

 is to move, and when it is to cease moving. All muscles 

 employed in moving the body are under the control of the 

 will of the individual. 



6. Fat. Outside the muscles, and often filling in the in- 

 equality of surface, there is, during the greater part of life, a 

 layer of adipose tissue or fat. This serves very important 

 purposes in the physical economy, and forms a valuable cover- 

 ing and cushion to the parts beneath. It also gives beauty to 

 the figure, by producing graceful form of limb and body. 

 The fat is contained in the cells of a structure known as 

 cellular tissue, which serves also as a connective tissue be- 

 tween parts. 



7. The Skin. The human body thus built up is covered 

 by the skin. The skin not only forms a protective covering 

 to the parts beneath, but, being possessed of nervous sensi- 



