pia

synonym: pia mater
https://doi.org/10.1351/goldbook.12010
Innermost of three membranous layers, together composing the meninges, that surrounds and adheres to the brain and spinal cord.
Source:
PAC, 2015, 87, 841. (IUPAC Glossary of terms used in neurotoxicology (IUPAC Recommendations 2015)) on page 897 [Terms] [Paper]