MUSCLE. 



83 



This tissue is found in the walls of the alimentary tract, in 

 the respiratory, urinary, and sexual organs, in the vessel walls, 

 in many glands, and in the skin. 



Fio. 49. 



Two heart muscle cells from the frog, isolated in KOH. In the upper cell one nucleus 

 is to be seen, in the lower cell two. At the ends of the nuclei the granular sarcoplasm is 

 collected, x 700. 



2. Heart Muscle. 



This has a place midway between smooth muscle and volun- 

 tary striated muscle. It might be called involuntary striated 

 muscle. In higher animals it consists of short rhomboidal or 

 cylindrical cells joined together end to end by means of a 

 cement substance, which may be dissolved in alkalies and nitric 

 acid. The cells usually are branched, as shown in Fig. 50. 



FIG. 50. 



Cement 

 substance 



Nucleus 



From a longitudinal section through human heart muscle. Two entire cells are to be seen. 

 The right one branches, x 500. 



They possess no cell membrane. In the middle of the cell 

 there is usually one nucleus, although there may be as many as 

 three or four. This nucleus is oval, vesicular, and surrounded 

 by a mass of undifferentiated protoplasm, in which there is 



