THE MUSCLES 



121 



FIG. 105. Fibers of Non-striated Mus- 

 cles, or Involuntary Muscles. 





structed exactly alike. Examined under the microscope, 

 each fiber of a voluntary muscle shows bright bands 



alternating with dark bands, 

 running across it (Fig. 103). 

 These bands give the whole 

 muscle a striated or striped 

 appearance under the mi- 

 croscope, hence this kind 

 of muscle is called striated 

 muscle (Fig. 104). The fi- 

 bers are bound together by 

 connective tissue into bundles called fascicles and these 

 again into larger bundles. The connective tissue surround- 

 ing the bundles can be plainly seen in 

 chipped beef, also in fresh beef and 

 boiled beef. The voluntary muscles are 

 darker red than the involuntary. Lean 

 meat is made up of these muscles. They 

 are near the surface, but their outlines 

 under the skin are obscured to a greater 

 or less degree in different persons, ac- 

 cording to the thickness of the layer of 

 fat between the muscles and the skin. 

 These muscles are usually attached to 

 bones. They contract quickly, while 

 the involuntary muscles contract slowly. 

 209. Involuntary Muscles are found 

 in the walls of the alimentary canal, the 

 bladder, the gullet and several other 

 organs ; all such muscles are composed 

 of fibers which are not striated, and are, therefore, called 

 plain muscle fibers. A striated fiber is about one inch in 

 length and yj^ of an inch in thickness and is shaped some- 

 what like a cylinder ; it possesses several nuclei. A plain 

 muscle fiber is not more than ^^U- of an inch in length, 



FIG. 106. Two Cardiac 

 Muscle Fibers. 



, nucleus; /, line of junc- 

 tion between the two cells ; 

 /, process joining a simi- 

 lar process of another cell. 

 (Magnified 400 diameters.) 



