We have shown you the Oracle Script of 疋, which is . It is quite obvious that 疋 is a drawing of a persons foot with his shank. Let us examine its evolution history to get a clear idea how it evolved. (image get from http://www.vividict.com)
Learn one Chinese Character a day - 疋
From above image, we can see clearly how it is slowly simplified from a complex drawing as till current 疋.
疋 is now no longer a standalone character, but a Radical.