ABSTRACT
When comparative studies were first made on mammals and the other animals, the researchers paid attention principally to differences in anatomy. It was only later, when technology improved, that they started to study comparative physiology and biochemistry. Galen (1) made the earliest recorded reference to the visceral nervous system in the second century. He gave the first account of the paravertebral sympathetic chains, but he made the mistake of describing the sympathetic and vagal trunks as one structure originating within the cranium. This gave rise to an error, which persisted for 1500 years. Galen was the first to note that the denervated heart maintained its beat. Following these observations of Galen, little progress was made through the ensuing 14 centuries until the time of Vesalius (1543) (2), who depicted a combined vagosympathetic trunk arising from the brain stem. Stephanos (1545) (3) and later Eustachius (1563) (4) were the first to distinguish the two separate nerves.
