FORM AND STRUCTURE OF MUSCLES. 



13 



called skeleton muscles. These muscles occur in various 

 forms. Sometimes they are flat, thin bands, and some- 

 times cylindrical cords, some of which are of considerable 

 length. Others again are thicker in the middle than at 

 the ends ; in these cases the middle is called the trunk, 

 the ends are spoken of as the head and tail, of the muscle. 

 Some muscles have two or more heads that is, two or 

 more ends springing from different points on the bone, 



easseoooos 



FlG. 4. SxitlATED Ml'SfLK-FIDRKS. 



a. Two fibres cut through in the middle, and passing, on the left, into tendons, b. A 

 single muscle-fibre deprived of its discs, ami separating into fibrillse. c. Two 

 single fibrilla;. d. A muscle-fibre separating into its discs. 



and uniting in a common trunk. But these muscles, 

 whatever their external shape, always consist of several 

 fibres, united into a bundle, and together forming the 

 muscle as a whole. One of these fibres, when isolated, 

 will be found to be very minute, and scarcely visible to 

 the naked eye ; when seen, enlarged from 250 to 300 

 times, under the microscope, it appears as a pouch, 

 consisting of a firm, solid wall, with certain contents ; 

 and this contained matter exhibits alternate lighter and 



LJ 



