This is a section of the cerebral cortex at the position of a sulcus (s). It shows the delicate arachnoid membrane (a) stretching across the sulcus from one convolution to another. Below the membrane is the subarachnoid space in which the cerebrospinal fluid circulates. It also contains loose trabecular tissue, comprising the pia mater. Note in the pia mater a number of small arteries and veins which supply the brain. Note also that the small vessels running into the brain are surrounded by spaces – extensions of the sub-arachnoid space on the surface. The section is stained with haematoxylin and eosin, and the photomicrograph is at magnification of X 80.

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