The Collaborative International Dictionary
Pia mater \Pi"a ma"ter\ [NL., fr. L. pia (fem. of pius tender, kind) + mater mother.] (Anat.) The delicate and highly vascular membrane immediately investing the brain and spinal cord.
Wiktionary
n. (context anatomy English) The innermost of the meninges, the membranes that surround the brain and spinal cord.
WordNet
n. the highly vascular innermost of the 3 meninges
Wikipedia
Pia mater ( or ), often referred to as simply the pia, is the delicate innermost layer of the meninges, the membranes surrounding the brain and spinal cord. Pia mater is medieval Latin meaning "tender mother". The other two meningeal membranes are the dura mater and the arachnoid mater. Both the pia and arachnoid mater are derivatives of the neural crest while the dura is derived from embryonic mesoderm. Pia mater is a thin fibrous tissue that is impermeable to fluid. This allows the pia mater to enclose cerebrospinal fluid. By containing this fluid the pia mater works with the other meningeal layers to protect and cushion the brain. The pia mater allows blood vessels to pass through and nourish the brain. The perivascular space created between blood vessels and pia mater functions as a lymphatic system for the brain. When the pia mater becomes irritated and inflamed the result is meningitis.
Usage examples of "pia mater".
The cerebrospinal fluid circulates through the various ventricles, and in the fourth ventricle escapes through tiny openings into the subarachnoid space outside the pia mater.
If you have a saint in your soul, I'm willing to bait him for you, but I'm damned if I'm going to meet you stumbling about with a candle inside my pia mater.
I presumed that the stitching had also sealed the gap in the dura and pia mater membranes.