|Diagrammatic transverse section of the medulla spinalis and its membranes. (At border, dura mater is black line, arachnoid mater is blue line, and pia mater is red line.)|
|The medulla spinalis and its membranes.|
|Gray's||subject #193 878|
The thin, mesh-like 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.
The pia mater is a neural crest derivative.