STRUCTURE AND COMPOSITION OF THE OUTER CONNECTIVE-TISSUE SHEATHS OF PERIPHERAL-NERVE

A regular pattern of parallel reflections with a periodicity of simila r to 39 mu m has been detected on peripheral nerve fascicles. The refl ections have been found to originate from a layer of wavy epineurial c ollagen fibrils arranged in register around the entire circumference o f the fascicle. The waves were observed to be disposed in parallel wit h the plane of the fascicular sheath and along its axis. The pattern w as observed in cut or relaxed fascicles in situ as well as in isolated and split layers of the epineurium. The pattern was not observed on n erve fascicles under tension. An additional structural feature consist ing of longitudinally disposed elastic fibres was also detected among the epineurial collagen fibrils. The perineurial collagen associated w ith sheets of cells was found to be disposed in flattened waves as in the inner layer of the epineurium. The period of the waves, however, w as much shorter, in the range of 6-9 mu m. From the nature of the wavy structure it can be surmised that on stretching or contraction the sh eath length may change, thus accommodating displacement and movement o f nerve fibres.