(Portland, OR)  --  Portland police say they've arrested a woman who's accused of biting her eleven-year-old son.  Officials say 30-year-old Heidi Lynn Boyum apparently bit her son as he tried to intervene in a fight between his mother and her boyfriend Saturday at a home on Southeast 148th Avenue.  Police say the boy had a large bite mark on his arm and several small cuts and scratches.  Boyum is charged with fourth-degree assault and first-degree criminal mistreatment.