How to enable wrapping after C-x 3

[ryofurue]

Hi emacs users,

I couldn't find this in the info or on the Internet.  By default,
long lines are wrapped and a tiny bent arrow is shown on
the right margin.  But, when you split the window by C-x 3
to have two windows side-by-side, long lines aren't wrapped.
Instead, tiny straight arrows are shown on the right margin,
and when you move the pointer (cursor) righward out of the
displayed region, the text scrolls horizontally.   How do you
have the original wrapping behavior in split windows?
How do you switch back and forth between the two
behaviors?  I use emacs 22.1 on the testing distribution
of Debian GNU/Linux.

Regards,
Ryo