<P> A longitudinal plane is any plane perpendicular to the transverse plane . The coronal plane and the sagittal plane are examples of longitudinal planes . </P> <P> Sometimes the orientation of certain planes needs to be distinguished, for instance in medical imaging techniques such as sonography, CT scans, MRI scans, or PET scans . One imagines a human in the anatomical position, and an X-Y-Z coordinate system with the y - axis going from front to back, the x-axis going from left to right, and the z - axis going from up to down . The z - axis is usually up (Tait - Bryan angles) and the right - hand rule applies . </P> <P> In humans, reference may take origin from superficial anatomy, made to anatomical landmarks that are on the skin or visible underneath . As with planes, lines and points are imaginary . Examples include: </P> <Ul> <Li> The midaxillary line, a line running vertically down the surface of the body passing through the apex of the axilla (armpit). Parallel are the anterior axillary line, which passes through the anterior axillary skinfold, and the posterior axillary line, which passes through the posterior axillary skinfold . </Li> <Li> The mid-clavicular line, a line running vertically down the surface of the body passing through the midpoint of the clavicle . </Li> </Ul>

What is the difference between midsagittal and parasagittal