Fibre size distribution in the elbow joint nerve of the cat.

The elbow joint nerve, a small branch of the musculocutaneous nerve in the cat, was investigated with low power transmission electron microscopy. By taking a series of overlapping photographs a montage was constructed of the cross section appearance of the complete nerve. Thus, a complete count of the number and sizes of myelinated and unmyelinated fibres was obtained. Two peaks in the distribution of myelinated fibres were consistently found, one at 2-5 micrometers and the other at 8-11 micrometers. The number of unmyelinated fibres was much larger than the number of myelinated fibres, with an average ratio of 4.4:1. This proportion of unmyelinated fibres is higher than that found by earlier workers, but is comparable with that in other peripheral nerves.