From the Greek sympathies sensitive, susceptible to influence.

Sympathetic nervous system - part of the autonomic nervous system, clusters of nerve cells or ganglia that are located along the spine and connected laterally to spinal nerves. It innervates blood vessels and other internal organs.

In higher crustaceans (Malacostraca) the sympathetic system is very pronounced. In the river crayfish, it represents two trunks, starting from ganglia lying on the ocolaryngeal commissures and merging to form a ganglion on the upper wall of the stomach. From this unpaired ganglion comes the unpaired nerve, giving branches to the stomach, liver, and heart. In some lower crayfish, weak trunks have also been observed coming from the commissures and having, perhaps, the significance of sympathetic trunks.

A considerable part of the nervous ganglia of molluscs, such as the buccal ganglia, which give nerves to the pharynx, salivary glands, esophagus, anterior aorta, and perhaps partly visceral ganglia, which give nerves to many internal organs, should probably be attributed to sympathetic. In cephalopods the buccal ganglion stands in connection with the unpaired ganglion lying in the region of the stomach and giving nerves to most of the intestines and liver. This latter ganglion is clearly sympathetic in character. For lack of physiological data to indicate the boundaries between the sympathetic system and the central system in molluscs is not always possible.