[TA] a delimited part or section of an organ or other structure that lies closest to the midline compared with the other similar parts or sections.medial bronchopulmonary segment S V, medial basal bronchopulmonary segment S VII, (left) medial hepatic segment [IV], (right) posterior medial hepatic segment [VIII], (right) anterior medial hepatic segment [V] SYN: segmentum mediale [TA].