1) Toward a middle plane 
• (adv.) Toward, or on the side toward, the mesial plane; mesially; -- opposed to laterad.
(me´ze-ad) toward the middle or center.
Mes'i·ad adverb [ Greek 
Type: Term Pronunciation: mē′zē-ad, mes′ē-ad Synonyms: mesad
mesiad Directed or proceeding toward the median sagittal plane of the body or, specifically, following the dental arch toward the center line.