✓ The human arachnoid granulation was studied by light microscopy in gapless serial sections after local postmortem perfusion of the subarachnoid space with glutaraldehyde. The smaller granulations are invested in a dural sheath several layers thick which is separated from the body of the granulation by a true subdural space. In larger granulations, there are restricted regions where the body of the granulation protrudes through the dura to enter the venous sinus directly.