Figure 5b. Photo showing the relationship of the arachnoid (AM, single arrow) easily separating from the dura mater (DM, double arrow) and its relation to the subarachnoid space (SS) and the pia mater (PM). This postmortem photo does not have subdural hematoma (SDH). The PM is closely attached to the brain (triple arrows). Hygroma forms in the SS. Chronic SDH compresses the subarachnoid space and remain closely adherent to the dural border cell layers, which supplies it with blood.