Inside Mouse, Outside Mouse

Once there was
an inside mouse and
an outside mouse.
One day they both
went on a trip. They
traveled up, down,
across, around,
through, between,
behind, over, and under,
until they finally met
in the middle.
Hello!

Are they old friends?
Or new friends?
Did they just meet
today?
Or do they visit
every day?
And what do you think
might happen next
to the inside mouse
and the outside mouse?