Ganglia ( G ; Galen, c173 ) : A ganglion is a recognizable aggregation of neurons (Waldeyer, 1891). There are marginal ganglia associated with invertebrate nerve nets, central ganglia associated with invertebrate central nerve cords, and peripheral ganglia in the invertebrate and vertebrate peripheral nervous system (Meckel, 1817). For vertebrates it has long been best practice to restrict the term ganglion (and terms derived from ganglion) to structures of the peripheral nervous system (Meckel, 1817). As Herrick wrote, "The term ‘ganglion' is also sometimes used for nuclei or centers within the brain…but this usage is objectionable, for the use of the word ganglion in vertebrate neurology should be restricted to collections of neurons outside the central nervous system, such as the ganglia of the cranial and spinal nerves and the sympathetic [autonomic] ganglia." (1915, p. 108). A prime example is the use of "basal ganglia" for cerebral nuclei (Swanson, 2000). Discovered and named in macrodissected adult mammals by Galen (c173; see translation by May , 1968, pp. 695-696).