  We consider four dimensional supersymmetric gauge field theories from brane
configurations with the matter content given by semi-infinite D4 branes ending
on both sides of NS branes. In M theory configuration, we discuss the splitting
of the M5 brane into infinite cylindrical M5 branes (which decouple) and
transversal M5 brane. The splitting condition appears naturally from the
consistency of the different projections of the Seiberg-Witten curve.
