. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 1372 VEIN. masses of white fibrous tissue are obliterated. When treated with this reagent the fibres of this coat lose their wavy character to a cer- tain extent, and present intersecting undula- tions. (Fig. 857. a.) When the internal coat is seen in transverse section, it presents a granular, indistinct appearance, without fibres of any determinate direction : in some places it presents lines of a crumpled or corrugated as- pect. In^. 858. a, this may be seen, as also its distinctness from the next coat, from which it
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 1372 VEIN. masses of white fibrous tissue are obliterated. When treated with this reagent the fibres of this coat lose their wavy character to a cer- tain extent, and present intersecting undula- tions. (Fig. 857. a.) When the internal coat is seen in transverse section, it presents a granular, indistinct appearance, without fibres of any determinate direction : in some places it presents lines of a crumpled or corrugated as- pect. In^. 858. a, this may be seen, as also its distinctness from the next coat, from which it is separated at one part by a slight interval. This coat appears to exist in all the veins, and in the smaller ones, and larger capillaries when treated with acetic acid, as hereafter to be described, its presence would seem to be indicated by the internal longitudinal nuclei, which are then displayed. Middle coat, of intermixed circular and lon- gitudinal fibres. — This tunic occupies about one-fourth of the entire thickness of the wall of a vein. Its internal boundary is sharp and distinct, where this coat is in contact with the internal, but the outer boundary, where it gra- dually merges into the external, is indefinite, and indeed artificial. In fig. 856. the middle coat is represented at b. and is composed of intermixed fibres of longitudinal and transverse yellow elastic tissue embedded in a nidus of white fibre. As this figure represents a longitudinal section, the transverse fibres of the yellow element Fig. Longitudinal vertical Section of Wall of Subclavian Vein of , treated with Acetic Acid. a, internal coat; b, middle coat; c, part of external coat. (Magnified 200 diameters.) are seen cut across, and appear as small discs : on the other hand, the longitudinal fibres with which they are mingled, are seen in pro- file, as interlacing and parallel rods : the former gradually diminish, and the latter, in the same proportion, increase, as viewed fur- ther an
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