branch of Regional_part_of relation which holds between subtrees of a tree organ that is either tracheobronchial or biliary or of arterial or neural type. 85994 arises from regional part of Segment of neural tree organ Segment of tracheobronchial tree Biliary tree Arterial anastomosis Systemic arterial tree Neural tree organ Pancreatic duct tree Root of median nerve Segment of biliary tree Tracheobronchial tree Conducting tissue of heart Arborial segment of arterial tree organ