94 



NORMA L IIISTOL G Y. 



essential for the functional activity of such organs as the stomach 

 and intestine. 



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

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

 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. 77 and 78). — 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 



Fro. 78. 



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Section of human heart. The direction of the section is such thatthe muscular cells are cut 

 exactly perpendicular to their long axes, a, intermuscular areolar tissue. From this, more 

 delicate fibrous tissue penetrates between the muscle-fibres forming the muscular bundles, 

 which are imperfectly separated from each other by the broader septa of fibrous tissue. 

 b, muscle-cell cut beyond the nucleus; c, cell cut so as to include the nucleus; d, cell cut 

 jus! below a branch. The index line d points to that part of the cell which passes into 

 the branch. The granular character of the contractile substance when seen in cross- 

 section has been omitted from the figure. At the lower edge of the figure the section 

 has been torn, but a small amount of the subpericardial areolar tissue is represented. 



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 

 of the nucleus. The rest of the cell-body is composed of contractile 



