Amacrine extension : A neuron extension that in a chain normally forms a reciprocal (bidirectional) synapse (Foster & Sherrington, 1897) with a like extension of another neuron (Waldeyer, 1891); that is, an amacrine extension may function as an axon (Kölliker, 1896) or a dendrite (His, 1889) in a chain, conducting in either direction depending on functional activity in the neural network; see Swanson (2003, pp. 23, 243). An amacrine extension may also form unidirectional synapses. A synonym is amacrine process.