In an experimental anatomic investigation carried out on cats and dogs, Kuntz and Farnsworth1 demonstrated nerve fibers of spinal ganglion origin in the gray communicating rami which join the nerves which supply the upper and lower extremities. These fibers are afferent components of the spinal nerves through the ventral roots of which the preganglionic fibers involved in the sympathetic innervation of the extremities reach the sympathetic trunk ganglions. Those which traverse the gray communicating rami which join the nerves to the upper extremity, therefore, are afferent components of the upper thoracic nerves, probably including the first to the fifth. Those which traverse the gray communicating rami which join the nerves to the lower extremity are afferent components of the lower thoracic and first and second lumbar nerves. These afferent fibers, like the preganglionic sympathetic components of the same nerves, enter the sympathetic trunk via the corresponding white communicating rami.
KUNTZ A, SACCOMANNO G. AFFERENT CONDUCTION FROM EXTREMITIES THROUGH DORSAL ROOT FIBERS VIA SYMPATHETIC TRUNKSRELATION TO PAIN IN PARALYZED EXTREMITIES. Arch Surg. 1942;45(4):606-612. doi:10.1001/archsurg.1942.01220040102011