The role of the arachnoid villus in the removal of red blood cells from the subarachnoid space

✓ The electron microscope examination of arachnoid villi from dogs after the subarachnoid injection of blood reveals that erythrocytes accumulate and degenerate in the villi. A continuous layer of endothelium separates the villus from the lumen of the sagittal sinus. No evidence for pores through the endothelium or for the passage of intact erythrocytes from CSF to blood through arachnoid villi has been found.