Reference Landmarks
In the clinical examination of the living subject, the position of the internal organs is defined with reference to a set of vertical and horizontal lines running through the surface of bony landmarks.
Some significant vertical lines are":
Mid-sternal line - in the median plane anteriorly
Mid-clavicular line - through the midpoint of the clavicle
Mid-axillary line - midway between the anterior and posterior axillary folds, formed from skin overlying muscles. If you raise your arms while looking in the mirror, the two folds are obvious;p but they can also be palpated very easily even with clothes on.
Median posterior line - in the median plane anteriorly
The horizontal position can be defined with reference to the ribs or, less easily, the vertebrae.