The sympathetic pathways to the muscles of the iris concerned with pupillary action have been described by many investigators both in animals and in man.* It has been generally agreed that the cell bodies of the preganglionic neurons are in the eighth cervical and the first and second thoracic (dorsal) levels of the spinal cord. The greatest number apparently are found at the first thoracic level. These preganglionic neurons leave the spinal cord, as recorded in the literature surveyed, mainly by way of the first and second thoracic ventral roots and enter the sympathetic chain at these levels via the rami communicantes. They pass cephalad through the inferior cervical or the stellate ganglion (a fusion of the first thoracic with the inferior cervical ganglion) to synapse with the postganglionic neurons located in the superior cervical ganglion. These latter fibers then pass via the carotid vessels or nasociliary nerves to the
PALUMBO LT. Upper Dorsal Sympathectomy Without Horner's Syndrome. AMA Arch Surg. 1955;71(5):743–751. doi:10.1001/archsurg.1955.01270170101019
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