ABSTRACT
The perineurial cells of the small nerve branch of the normal human abdominal wall are observed with electron microscope. The fibrous long-spacing bodies (FLS) are found within the interstitial substance of the endoneurium. 1. 2-5 layers of the perineurial cells surround the nerve fasciculus. The perineurial cells are squamous in shape and the cytoplasm contains microfilaments and pinocytotic vesicles. Each perineurial cell has an obvious basement membrane on its basal surface but the fibroblasts, whatever situated in the endoneurium or on the outer surface of the perineurium, has no basement membrane. Numerous desmosome and some gap junctions between the close attached perineurial cells are demostrated. The collagen fibrils between perineurial cells can be often shown. FLS bodies and collagen fibrils about 45 nm in diameter in the interstitial substance of endoneurium inside perineurial cells are demonstrated. In the connective tissue surrounding the outside of perineurial cells, the collagen fibrils of 80 nm in diameter can be seen, but no FLS bodies present there. 2. FLS bodies in the endoneurial matrix can be demostrated. Most of them closely associated with the basement membrane of the Schwann cells surrounding the unmyelinated nerves but no FLS bodies are found associate with those of the myelinated nerves. A few FLS bodies do not relate to basement membrane and they are invested only with the collagen fibrils. In the longitudinal sections, most of FLS bodies are in spindle shape of various sizes, their longitudinal axes parallel to that of the adjoining collagen fibrils. Sometimes the FLS bodies continue with the collagen fibrils are found. Occasionally, FLS body like a bridge locate between two Schwann cells and its dark bands continue to the basement membrane of the Schwann cells. Two or three FLS bodies may fuse together but their cross bands do not registered at the same level. In the oblique sections, FLS bodies are nearly rectangular in shape, with the cross bands shown, and their appearance do not show greaty difference from those in longitudinal sections. The periodicity of FLS bodies is about 133nm in length; the dark band in it is about 53 nm, which is made of the dense granular substance; the light band is about 80 nm, which is made of a network with approximated parallel microfilaments. There are no further crossstriated structures within the periods. Some problems, such as the role of the perineurial cells, the relationship of FLS bodies with basement membrane, are briefly discussed.