Abstract
The vascular pattern of the thymus of the mouse was observed with the light and electron microscope. The present finding of the general vascular pattern was essentially the same as previously reported by SMITH, THATCHER, KRAEMER and HOLT (1952). The thymic vessels in the cortex are, for the most part, capillaries and those in the medulla, venules and veins. In electron microscopy the cortical capillaries possess the same structural features as are generally known for common capillaries. The cortical capillaries are surrounded by pericapillary spaces. The spaces are bordered by a layer of cytoplasmic extensions of epithelial reticular cells. However, since the lining epithelial cell layer is not continuous with frequent interruption, the pericapillary spaces communicate directly with the intercellular meshes of the cortical tissue. Therefore, no morphological evidence suggests complete isolation of lymphocytes from the blood vessels. In the medulla, the veins are also surrounded by a wide space. The space is limited by a layer of epithelial reticular cells, but the epithelial layer often possesses intercellular gaps, by which the perivascular spaces communicate with the intercellular meshes of the medulla. The finding is discussed with regard to transfer of thymic lymphocytes.
