pia mater

English Thesaurus

1. the highly vascular innermost of the 3 meninges (noun.body)

hypernym	:	meninges, meninx,
definition	:	a membrane (one of 3) that envelops the brain and spinal cord (noun.body)

part meronym	:	leptomeninges,
definition	:	the two innermost layers of the meninges; cerebrospinal fluid circulates between these innermost layers (noun.body)