Views of the endothelial surface of the marginal sinus in rat spleens using the scanning electron microscope

The cell-passing pores and the endothelial surface of the marginal sinus of the rat spleen were studied using a scanning electron microscope. The cell-passing pores were observed to be limited to the endothelial junction of the marginal sinus on the marginal zone side. They were so large that blood cells might easily pass through them. The cell-passing pores were thought to be the main pathway for blood cells moving from the marginal sinus to the marginal zone. The endothelial surface was relatively smooth, although some granular microvilli were distributed irregularly on the surface. At the endothelial junction, microvilli-like projections lined the junctional edge.