Fig. 3
From: The glymphatic hypothesis: the theory and the evidence
Meningeal layers associated with a cortical penetrating artery and an emerging vein. This is based on evidence obtained using electron microscopy. Note that the artery has a pial sheath as it courses along the surface of the cortex and this sheath follows the artery without break as it penetrates the cortex. By contrast the sheath around the emergent vein is not present along the course within the cortex. A, arachnoid membrane; SAS subarachnoid space (which on the dorsal surfaces of the cortex may be collapsed other than where it covers a blood-vessel); PF pial perforations. For more recent discussion of the presence (arterial) or absence (venous) of a pial sheath within the parenchyma see [127]. Reproduced with permission from Zhang et al., J. Anat. 1990 [100]