Abstract
Summary
The total number of nerve fibers enumerated in 18 normal sympathetic trunks, varied from 5404 to 10127. In 15 of the 18 nerves the myelinated exceeded the unmye-linated axons but in the majority of the 15 nerves the excess of myelinated over unmye-linated axons is not great. In only one instance was the trunk almost completely com-posed of myelinated fibers (96%).
A variable number of nerve fibers (111 to 2619) remains in the cervical sympathetic trunk after its preganglionic axons have been eliminated. These residual fibers comprise 2 to 33% of the total number of nerve fibers in the cervical sympathetic trunk and the majority of them are unmyelinated.
The majority (67 to 98%) of the nerve fibers in the cervical sympathetic trunk are preganglionic axons from thoracic levels of spinal cord. Considerable variation exists in the ratio between myelinated and unmye-linated preganglionic axons in different cats, the unmyelinated ranging from 1 to 61% and averaging 34%.
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