part of part of has part has part located in located in bounding layer of bounding layer of collagen trimer perineurium http://upload.wikimedia.org/wikipedia/commons/9/9c/Gray636.png NCIT:C33302 UMLS:C0205890 Connective tissue surrounding a fascicle[Wikipedia:Perineurium]. Wikipedia:Perineurium NCIT:C41407 consider FBbt:00007090 (perineurium): The outer two layers of glial cells that cover the central nervous system and the nerves. The outer layer is the perineurial sheath (sometimes referred to as the perineurial sheath outer layer); the inner layer is the sub-perineural glial sheath (sometimes referred to as the perineurial sheath inner layer) SCTID:362299001 NLXANAT:090205 A layer of thin, concentrically arranged cells with interspersed collagen that lies within the epineurium. The perineurium is a component of the blood–nerve barrier and is essential for protecting axons and their associated Schwann cells from ionic flux, toxins and infection. FMA:52585 EMAPA:37849 BTO:0003153 perineurial UBERON:0000121 epineurium nervous system nerve fasciculus blood nerve barrier dense irregular connective tissue