Anatomical "lines", or "reference lines," are theoretical lines drawn through anatomical structures and are used to describe anatomical location. The following reference lines are identified in Terminologia Anatomica:
Anterior median line
Lateral sternal line: A vertical line corresponding to the lateral margin of the sternum.
Parasternal line: A vertical line equidistant from the sternal and mid-clavicular lines.
Mid-clavicular line: A vertical line passing through the midpoint of the clavicle.
Mammillary line
Anterior axillary line: A vertical line on the anterior torso marked by the anterior axillary fold.
Midaxillary line: A vertical line passing through the apex of the axilla.