Left human lung with visible hilum. The left lung (pulmo sinister) is divided into two, the right lung (pulmo dexter) into three lobes (Lobi pulmonis). The lobes can be divided further into 19 lung segments (Segmenta bronchopulmonalia), each of which are supplied by a segmental bronchus and a segmental artery. The right lung is composed of 10 segments, the left lung of 9 segments.