A note on the limb nerves of the frog (Rana tigrina).

In the frog (Rana tigrina) the mean length of the brain was 17.5 mm and that of the spinal cord 61 mm. The weight of the brain and spinal cord (together) was 389 mg. The fascicular number, fascicular area, total number of fibres and their density were studied in the left and right brachial nerves, left and right sciatic nerves and the sympathetic trunk (nerve). The largest number of nerve fascicles (12) was noticed in the sympathetic trunk while the right brachial nerve comprised of only one nerve fascicle. As for the mean fascicular area, the left brachial nerve had the greatest area (0.7963 mm2) while the least (0.1312 mm2) was noticed in the sympathetic trunk. The sympathetic trunk revealed the highest number (mean value 2176) of myelinated fibres. The least value in this regard (598) was noticed in the left sciatic nerve. As for the external diameter of the nerve fibres, more than 50% of the fibres in all the nerves were of the order 6--8 micrometer. The histograms confirmed this trend. The greatest density of myelinated nerve fibres was noted in the left brachial nerve (288/mm2). Based on the retrograde degeneration, the ventral horn neurons giving origin to the motor fibres in the brachial nerves were traced to spinal cord segments 2 (Preponderantly) and 3. The ventral horn neurons of spinal cord segments 7 and 8 appear to contribute motor fibres to the sciatic nerves.