part of ends during starts during brain death tissue pia mater UBERON:0002361 The innermost delicate fibrous meningeal coverings of the CNS. It is closely adherent to the brain tissue and is composed of one to several layers of flattened, modified fibroblasts and the ECM (collagen and elastic fibers, etc.) they produce. XAO:0005289 pia matter pia xenopus_anatomy NF stage 22