Add outgoing dendrite

The command Add outgoing dendrite can be applied to It is available in the context menue of these nobs.
 * dendrites - a knotwith one incoming an d two outgoing pipes is created
 * knots with only one outgoing dendrite (knots with two outgoing dendrites cannot have a third one)

Hint: Normal neurons can by definition have only one output dendrite, the axon. Therefore neurons do not provide this command.