378 



MUSCULAR ACTION 



artifacts by others, and hence the matter, so important for the physi- 

 ology of muscle, must be a little longer considered in doubt. The free 

 transmission of the contraction-wave, for example, in hollow organs like 

 the ureters, makes probable some such mode of connection between the 



FIG. 231 



The smooth muscle in the bronchioles of the dove's lung. (Eberth.) 



various cells and bundles whether the staining methods at present,, in 

 use show such connections clearly or not. Each fiber-cell is surrounded 

 by a very delicate transparent sheath which wrinkles more or less when 

 the fiber changes its shape in contracting. 



CROSS-STRIATED MUSCLE is the variety most fully under the will's 

 control, and it is therefore often called voluntary muscle; it is frequently 

 attached to the bones and hence is sometimes termed skeletal muscle. 



FIG. 232 



Nucleus- 



Intercellular 

 bridges' 



Longitudinal section in the smooth muscle of a dog's large intestine, to show especially the 

 intercellular bridges. 530 /i- (Szymonowicz and MacCallum.) 



Cross-striated muscle, like the smooth sort, is made up of fusiform 

 cells. These are, however, apparently of much greater structural com- 

 plexity and differ much from the others in size and mode of action. The 

 fibers or cells (each fiber being apparently a highly specialized cell), of 

 cross-striated muscle, are more or less cylindrical in shape. In size they 

 may be even as much as 12 c.m. long and 0.1 wide, and they are thicker 

 in the male than in the female. Roughly speaking, the fibers are smaller 



