These, then, are the parts common to the male and the female sex.
The relative position of the parts as to up and down, or to front
and back, or to right and left, all this as regards externals might
safely be left to mere ordinary perception. But for all that, we
must treat of them for the same reason as the one previously brought
forward; that is to say, we must refer to them in order that a due and
regular sequence may be observed in our exposition, and in order
that by the enumeration of these obvious facts due attention may be
subsequently given to those parts in men and other animals that are
diverse in any way from one another.