Noun
The delicate and highly vascular membrane immediately investing the brain and spinal cord.
Source: Webster's dictionaryBlood vessels enter the central nervous system through the perivascular space above the pia mater. Source: Internet
Between the arachnoid mater and the pia mater is the subarachnoid space which contains cerebrospinal fluid (CSF). Source: Internet
The pia mater and arachnoid mater including blood vessels are seen at the top of the image. Source: Internet