part of attached to portion of tissue perineurial glial sheath Evidence of mesodermal origin comes from the observation that embryos lacking mesoderm lack this cell layer and the overlying neural lamella (Edwards et al., 1993). apical glial cell perineurial sheath The outermost cellular layer of the nervous system, probably of mesodermal origin (Hartenstein and Jan, 1992). This layer consists of glial cells, which participate in nutrient uptake and establish a first diffusion barrier (Limmer et al., 2014). neural lamella VFB:FBbt_00007089 FBbt:00007089 fly_anatomy.ontology perineural sheath perineurium subperineurial glial sheath