Fibers in the ventral spinal nerves of the frog

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Abstract
The use of the electron microscope provides accurate data of the number, size, and distribution of fibers in nerve tissue. Nerve fiber counts determined by electron microscope mapping show increases of two to seven times in the number of fibers over those determined by light optics. The combined counts of fibers, on one side in Rana pipiens, from the ventral spinal nerves (1, 2, and 3) supply the forelimb with 14,000 fibers; from spinal nerves (4, 5, and 6) to the trunk, 4,050 fibers; and over 20,000 fibers from the ventral spinal nerves (7, 8, 9, and 10) pass into the sciatic and crural nerves which innervate the hind limb. The greatest total number of fibers, and especially of small and fine fibes, are in the second and ninth spinal nerves. Of all the nerves studied, the sciatic contains the greatest number of fibers (16,500). The high numbers and percentages of fine and small fibers in the spinal, sciatic, and crural nerves emphasize the importance of determining the function of these fibers.