Pia mater

The pia mater (Latin: "tender mother", itself a translation from Arabic) is the delicate innermost layer of the meninges - the membranes surrounding the brain.

The pia mater closely envelops the entire surface of the brain, running down into the fissures of the cortex. It joins with the ependyma which lines the ventricles to form choroid plexuses that produce cerebrospinal fluid.