TISSUES OF SPECIAL FUNCTION. 89 



Smooth muscular tissue occurs in the form of bundles or layers, 

 in each of which the cells or fibres run in the same direction. The 

 tapering ends of the individual cells interdigitate with each other, 

 masking the intercellular substance, so that the tissue appears as 

 though wholly composed of cells. Surrounding the muscular 

 bundles or between the layers of that tissue is vascularized areolar 

 tissue, giving it support and containing its nerve-supply. 



The microscopical appearances of sections of smooth muscular 

 tissue depend upon the direction in which the individual cells have 

 been cut. A brief analysis of the different appearances that may 

 result will be useful as an illustration of the way in which micro- 

 scopical appearances must be interpreted in order to gain a correct 

 conception of the structure of an object under observation. It is 

 rarely that sections happen to be made in such a direction that they 

 reveal the complete structure of an object. It is nearly always 

 necessary to study the appearances presented by the section, and to 

 infer what the structure of the object must be in order to yield the 

 appearances seen. This is sometimes a matter of considerable 

 difficulty. 



If the plane of the section lie parallel with the long axes of 

 the cells, the nuclei of the latter will appear as rod-like or long, 

 oval bodies lying parallel to each other and distributed at regular 

 intervals throughout the tissue. The outlines of the cells will be 

 distinctly visible in some places, but in most of the section the 

 boundaries of the deeper cells will be obscured by the bodies of 

 the cells at the surface of the section, and the borders of the latter 

 will be difficult of detection, because in many places the knife has 

 left only a portion of the cell with a very thin and transparent 

 edge (Figs. 72 and 73). For the practical recognition of the tissue, 

 when cut in this direction, we must, therefore, in many cases, 

 depend solely upon the shape and distribution of the nuclei and 

 the color of the material between them after the section has been 

 treated with certain stains (e. g., eosin). 



If the cells of the tissue have been cut perpendicular to their 

 long axes, the section will contain true cross-sections of the indi- 

 vidual fibres. These appear as round, oval, or, more usually, 

 polygonal areas of various size, according to the part of the cell 

 included in the section. If the cell has been cut near one of its 

 ends, the cross-section will be small ; if near the middle, it will be 

 large, and will contain a cross-section of the nucleus, situated near 



