Graphic-digitizer analysis of axon spectra in ethmoidal and lingual branches of the trigeminal nerve.

Sections were removed from the lingual and ethmoidal nerves of cats and histologically prepared, and the fibers were analyzed under the light microscope. Neural dimensions were measured by a new technique, employing a graphic digitizer and computer. The outline of a neural structure was traced with the digitizer pen, and the total number of axons, their cross-sectional areas, shapes, diameter spectra, and locations within the nerve were calculated. Both nerves had unimodal axon spectra with the peak between 2 and 6 mum diameter. Differences in axon composition occurred over the diameter range of 9 to 20 mum; the lingual nerve had many axons in this range, the ethmoidal nerve only a few. The total number of myelinated axons was near 4000 in the lingual nerve, near 1400 in the ethmoidal nerve; only the latter had many large-sized Remak bundles (containing C-fibers). Most myelinated axons were not perfectly circular but exhibited various degrees of distortion.