Muscles and Motion. 



i - 13- Two Striated Muscle 



Fibers showing the termina- 



tions of the Nerves 



Microscopic Structure of Muscle. If a tiny shred of 

 muscle, such as you may remove from the teeth with a 

 toothpick, be put in a drop of slightly 

 salted water and examined under a 

 good microscope, the fibers may be 

 seen. These are small thread-like 

 bodies, with cross markings, from 

 which they are called (striated or 

 striped muscle fibers^ From the fact 

 that they are under the control of the 

 will they are called voluntary muscle 

 fibers. 



Plain Muscle Fibers. In the walls 

 of the arteries, of the gullet, stomach, intestines, and 

 elsewhere, there are muscle fibers of a different kind 

 from those of the skeleton. These fibers are spindle- 

 shaped cells, as shown in Fig. 14, with a nucleus near 



the center, and do not have the 

 cross-markings. Hence they are 

 called //tfz>/, smooth, or |m-striated^ 

 ... isolated Fibers muscle fibers. Owing to the fact 

 that they are not under the control 



Fibers Joined Q ^ w j U they ^ Q c ^ Qd i m , l un . 



tary muscle fibers. 



Heart Muscle. The fibers which 

 make up heart muscle are different 

 Plain mnstriated) Muscle in appearance from either the stri- 

 ated or the smooth muscle fibers. 



They are more or less branched, as shown in Fig. 15. No 

 sheath has been found on these fibers. 



The Three Kinds of Muscular Fibers Compared. The 



striated fibers are called voluntary, and the plain fibers 



Fig. 14. 



