TISSUES OF SPECIAL FUNCTION. 



89 



in conferring "tone" to certain structures in which it is found, 

 notably the walls of the arteries and veins. They also render it 

 of service in producing the vermicular movements that are essential 

 for the functional activity of such organs as the stomach and intes- 

 tine. 



Smooth muscular tissue has a wide distribution in the body. It 

 is found in greatest bulk in the uterus, middle coats of the arteries 



FIG. 74. 



Diagrams of cardiac muscular tissue. 



A, longitudinal section: a, nucleus of muscle-cell ; 6, unmodified cytoplasm; c, contractile 



substance with longitudinal and transverse striations ; d, cement-substance uniting con- 

 tiguous cells ; e, areolar tissue (vessels omitted) between the muscle-fibres formed by the 

 union of the individual cells ; /, small bloodvessel within the areolar tissue. If the lines 

 of junction between the cells were not visible, the tissue would appear as though com- 

 posed of interlacing and anastomosing fibres, none of which could be traced for any con- 

 siderable distance. Such is the usual appearance of longitudinal sections of cardiac 

 muscle. 



B. transverse section : a, section of a cell, including the nucleus ; c, section above the nucleus 



and just below a crotch formed by the divergence of a branch; 6, section above the 

 nucleus and the point where the branch V is given off. 



and veins, the muscular coats of the stomach and intestine, and the 

 wall of the bladder ; but we shall find it present in greater or less 

 amount in many of the organs, the structure of which we shall 

 presently have to study. 



2. Cardiac Muscular Tissue (Figs. 74 and 75). The heart-muscle 

 is composed of cells having a general cylindrical form and contain- 

 ing a single (occasionally, two) nucleus. The nucleus is vesicular, 

 has a distinct reticulum of chromatin, and is usually oval. It is 

 situated near the centre of the cell, and is surrounded by a small 

 amount of cytoplasm, which is a little more abundant at the ends 



