12 PHYSIOLOGY OF MUSCLES A?s"D NEKVES. 



CHAPTER II. - 



1. Muscles, their form and structure ; 2. Minute structure of 

 striated muscle -fibres ; 3. Connection of muscles and bones ; 

 4. Bones and bone-sockets; 5. The law of elasticity; 6. Elas- 

 ticity of the muscles. 



1. Muscles are elastic structures capable of altering 

 their form — that is, of becoming shorter and thicker. 

 In the bodies of the more highly developed animals 

 they constitute those masses which are commonly called 

 flesh. The flesh, when carefully studied, is found to 

 consist of bundles of fibres, the ends of which are pro- 

 duced into white cords, most of which are attached to 

 bones. When one of these muscles shortens, it exerts 

 a strain, by means of these white cords, on the bones ; 

 and these latter, being movable the one against the 

 other, are thus put in motion by the shortening of the 

 muscle. All muscles are not, however, arranged in this 

 way ; some ring-shaped muscles form the walls of sacs 

 or pouches, and these, by contracting, decrease the 

 space within these cavities, so that the contents of the 

 latter are thus forced onward. In any case, muscles 

 always serve to produce movement — either of the limbs 

 in opposition to each other, or of the whole animal, or 

 of the substances contained within the cavities. 



We must first confine our attention to those muscles 

 which are attached to bones, and which are therefore 



