52 PHYSIOLOGY. 



Plain and Striated Muscle Fibers Compared. These plain mus- 

 cle fibers are further like those of the skeletal*muscles in that they are 

 under the control of the nerves, but they are involuntary in their action. 



PIGMENT 

 CELLS 



ARTERY 

 Fig. 22. Part of Frog's Web (low magnifying power). 



We cannot interfere with the action of these muscles, no matter how 

 strongly we may will to do so. Without our thinking about it, more 



