The present study is an electron microscope analysis of the rami communicantes and its purpose is to determine the functional categories of unmyelinated axons in these nerves. Our findings indicate that the grey rami of segments T7, T8, or T9 in the cat consist of approximately 5,000 unmyelinated axons and 20 myelinated axons, and that these axons are post‐ganglionic sympathetics. Although the numbers are new data, this conclusion confirms classic work. The white rami from the same segments contain approximately 3,200 unmyelinated axons and 1,600 myelinated axons. 80–90% of the myelinated axons are preganglionic sympathetics and the remainder are presumably sensory. This conclusion is also in confirmation of classic work. The new conclusions are that approximately 30% of the unmyelinated axons are preganglionic sympathetics, approximately 60% seem to be post‐ganglionic sympathetics and the surprisingly small remainder may be sensory.
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