272 MUSCLES 



mysium. If we proceed further, and cut across the end 

 of one of these bundles, or fascicuh, we find it to be divided 

 into smaller bundles by perimysium partitions, and these, 

 in turn, into still finer partitions and bundles. These 

 ultimate bundles may be teased apart into a certain 

 number of microscopic muscle fibers too small to be 

 examined with the naked eye. These fibers are the struc- 

 tural elements of the muscle. It is the combined contrac- 

 tion and expansion of these fibers that produces the com- 

 plete muscle action. 



Microscopic structure of striated muscle. — Each muscle 

 fiber, when examined under the microscope, is found to 

 be from J inch to IJ inches in length, but only i^^q- inch 

 to jjQ inch in diameter. Thej' are spindle-shaped and 

 taper to a point at each end. They evidently do not 

 extend the entire length of the bundle, which may be a 

 foot or more in length, but are packed together, side by 

 side, the pointed ends of one fiber fitting in between the 

 ends of others, so that each fiber extends lengthwise of 

 the bundle. 



The fiber of a striated muscle may always hz recog- 

 nized by its striped or striated appearance. These stripes 

 extend transversely across the fiber and pass entirely 

 through it. They are of two kinds, a broad, bright band, 

 and a narrower, darker band. These dark and bright 

 bands alternate. With the high powers of the micro- 

 scope can also be made out dim longitudinal striations. 



If we press upon one of these fibers with a needle point 

 it is seen to be covered with a transparent membrane or 

 sarcolemma which surrounds the striped, contractile, 

 inner substance. This outer coat or sarcolemma is a 

 tough transparent membrane. Visible through the sar- 



