in taxon composed primarily of Mammalia leptomeninx pia mater http://upload.wikimedia.org/wikipedia/commons/3/31/Gray770-en.svg http://upload.wikimedia.org/wikipedia/commons/6/65/Gray770.png delicate innermost layer of the meninges-the membranes surrounding the brain and spinal cord. 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. In the spinal cord, the pia mater attaches to the dura mater by the denticular ligaments through the arachnoid membrane. The pia mater is a neural crest derivative[Wikipedia:Pia_mater]. EHDAA:2833 EHDAA:1961 EHDAA:1367 RETIRED_EHDAA2:0001464 SCTID:362305004 NLXANAT:090209 GAID:693 MA:0001116 EMAPA:32663 EHDAA:2001 EHDAA:6566 EHDAA:6583 EHDAA:3692 UMLS:C0031869 EHDAA:2867 pia mater of neuraxis EHDAA:2685 Wikipedia:Pia_mater EHDAA:3710 BTO:0001635 MESH:D010841 UBERON:0002361 pial membrane neuronames:1463 The innermost layer of the leptomeninges, consisting of a delicate membrane closely covering the surface of the brain and spinal cord,and lying under the arachnoid membrane. The pia, unlike the arachnoid, extends into the sulci in gyrencephalic animals. NCIT:C33321 FMA:9590 EHDAA:2099 pia EHDAA2:0004318 consider adding adjacency relationship to neuraxis (brain+spinal cord); however note that at this time the meninges may be considered part of the nervous system loose connective tissue