Endoneurium

The nerve fibers are held together and supported within the funiculus by delicate connective tissue, called the endoneurium.

It is continuous with septa which pass inward from the innermost layer of the perineurium, and shows a ground substance in which are imbedded fine bundles of fibrous connective tissue, primarily collagen, running for the most part longitudinally.

It serves to support capillary vessels, arranged so as to form a net-work with elongated meshes.

It is found in other places too, such as surrounding the Schwann cells on the peripheral side of the transitional zone on the auditory nerve. (citation: JP Fraher. The Transitional zone and CNS regeneration. J Anat,2000,196:137-158.)