a delimited part or section of an organ or other structure which lies in front of or ventral to the other similar parts or sections. 1) segmentum anterius (hepar) [NA]; the anterior segment of the right lobe of the liver. 2) segmentum anterius (pulmo dexter et sinister) [NA]; [S 3]; the anterior segment of the superior lobe of the right and left lungs. 3) anterior segment of the eye; the intraocular segment of the eyeball occupied by the aqueous which lies in front of, and is separated from the vitreous-filled posterior segment by, the lens and zonule; it is subdivided by the iris into anterior and posterior chambers. Syn: segmentum anterius.