Tryptic digestion of the retina with subsequent staining by suitable dyes has permitted
identification of two types of cells associated with the capillary wall. One type is the
endothelial cell lining the lumen. The other type we have elected to call the mural cell
because it is encased within the vessel wall, covered on both its inner and outer surfaces by
basement membrane. At the present writing we are unable to state whether or not mural
cells comparable to those in the retinal capillaries exist elsewhere in the body; we have not …