long axis of body

long ax·is of bod·y

the imaginary straight line in the median plane that nearly intersects the center of all transverse planes through the body, running from the apex of the cranium through the center of the perineum and continuing between the lower limbs, parallel to and equidistant from the long axes of the limbs; in theory, this is the line about which the body's mass is equally distributed.
See also: embryonic axis. Synonym(s): cephalocaudal axis