Figure 1

Structures of the brain considered in this review. a) Mid-sagittal section from nose to the back of the head incorporating images of the lateral ventricles that lie to each side of the section. CSF filled spaces are shown in blue, blood filled spaces in pale red. The choroid plexuses are shown in darker red. b) Enlarged view of surface of a lateral ventricle at (E). c) Enlarged view of the cortical surface at (F). The glia limitans is a mat of glial processes. d) Drawing showing the relationships between the arachnoid membrane, the pia mater, the subarachnoid space, and the vasculature supplying the cortex. As described by Zhang et al. for the artery “the sheath has been cut away to show that the periarterial spaces (PAS) of the intracerebral and extracerebral arteries are in continuity. The layer of pial cells becomes perforated (PF) and incomplete as smooth muscle cells are lost from the smaller branches of the artery. The pial sheath finally disappears as the perivascular spaces are obliterated around capillaries (CAPS). Perivascular spaces around the vein (right of picture) are confluent with the subpial space and only small numbers of pial cells are associated with the vessel wall” [23]. The cortical boundary along these vessels is formed by glial foot-processes. The graphic elements in a) and b) and in c) with minor extensions are taken with permission from Figure one of Strazielle et al.[19] and relabelled. d) is reproduced with permission from Figure ten in [23] and partially relabelled. R.O. Weller (personal communication) has emphasized that the spaces shown between the arterial wall and the pial sheath and between the sheath and the glial end-feet were virtual spaces in their electron micrographs. The periarterial spaces are also portrayed in Figure 6.