ganglion

Solid cluster of nervous tissue containing many cell bodies and synapses, usually enclosed in a tissue sheath; found in invertebrates and vertebrates.

In many invertebrates, the central nervous system consists mainly of ganglia connected by nerve cords. The ganglia in the head (cerebral ganglia) are usually well developed and are analogous to the brain in vertebrates. In vertebrates, most ganglia occur outside the central nervous system.

ganglion

In medicine, harmless swelling or cyst developing within a tendon sheath, usually at the wrist.