Chrysler and Ford also used air injection. Depending on the year and emissions package, all manufacturers use air injection to help the catalytic converter fully burn the exhaust gasses by injecting air into the cylinder head(s) downstream of the exhaust port, into the exhaust manifold(s), into the exhaust pipe, and into the catalytic converter itself.
I suspect multiple tubes going into the exhaust manifold ar air injection tubes. Really, air injection is a good thing that does not harm performance in any way and really helps cleanup the exhaust.