Horizontal, referring to the plane of the body, perpendicular to the vertical plane, at right angles both to the median and coronal planes, that separates the body into upper and lower parts. [L.]
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hor·i·zon·ta·lis (hor″ĭ-zon-taґlis) [TA] horizontal: a term denoting relationship to this orientation when the body is in the anatomical, i.e., the upright, position.Medical dictionary. 2011.