In $\triangle ABC$ , $\angle C=90^\circ$

In triangle $ABC$ , $\angle C=90^\circ$ ; the internal bisectors of $\angle A$ and $\angle B$ meet $BC$ and $CA$ at $P$ and $Q$ respectively. $M$ and $N$ are the feet of the perpendiculars from $P$ and $Q$ to $AB$ . Find the measure of $\angle MCN$ in degrees.