44 ELEMENTARY PHYSIOLOGY 



In fact, as we shall see, the ventricles have more work 

 to do than the auricles, and the left ventricle more to do 

 than the right. Hence the ventricles have more muscular 

 substance than the auricles, and tlie left ventricle than the 

 right ; and it is this excess of muscular substance which 

 gives rise to the excess of thickness observed in the left 

 ventricle. 



The muscular fibres of the heart are of a peculiar 

 nature, resembling those of the chief muscles of the body 

 in being transversely striated, but diflering from them in 

 many other respects. 



Pio. 15.— Cardiac Fibre Cells. 



Two cells isolated from the heart. . n, nucleus ; I, line of junctioa 

 between the two cells ; p, process joining a similar process of anotliei" 

 cell. (Magnified 400 diameters.) '■ 



Cardiac Muscular Tissue. — The muscular tissue of 

 the heart is intermediate in character between striated and 

 non-striated muscle. Like the non-striated muscle, it is 

 composed of cells, each containing a single nucleus, and 

 possessing no sarcolennna. But the cells (Fig. 15) are 

 generally short and broad, frequently branched or irregular 

 in shape, and their substance is more or less distinctly 



