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Abstract

The postganglionic neurons in four human superior cervical sympathetic ganglia and the preganglionic axons in the trunks just caudal to these ganglia were counted. The number of postganglionic neurons varied from 760,370 to 1,041,652. The estimates of the number of preganglionic fibers ranged from 5,305 to 12,008. The resulting ratio of preganglionic to postganglionic neurons was as high as 1 to 63 in one ganglion and as low as 1 to 196 in another. The number of postganglionic neurons in human superior cervical sympathetic ganglia is approximately ten times greater than the figure obtained in the cat and 20 times greater than in rabbit ganglia. The number of preganglionic axons does not vary proportionally and is of the same order of magnitude in cat, dog and man.