A 27-year-old Hyde Park man is facing charges that he beat his infant son, fracturing two bones in the baby's legs and seven of his ribs, Suffolk County prosecutors said today.

Christopher Duncan was ordered held on $25,000 cash bail at his arraignment Tuesday in West Roxbury District Court on charges of assault and battery on a child, assault and battery on a child causing serious injury, and mayhem.

Prosecutors said Duncan inflicted the injuries on his baby over the course of at least three months.

Duncan allegedly told witnesses that the baby had been crying, he grew frustrated, and he snapped the victim's legs.

"If you have a crying baby and you find yourself losing patience, please take a few minutes to cool down," Suffolk District Attorney Daniel F. Conley said in a statement.

The injuries were discovered when Duncan and the mother of his two children took the baby, who was three months old at the time, to Boston Medical Center on July 8. An investigation ensued, which resulted in police obtaining a warrant for Duncan's arrest on Monday.

The baby, along with Duncan's other child, a 17-month-old, is in the custody of the maternal grandmother, said district attorney's spokesman Jake Wark.

Prosecutors said parents who are feeling stressed can call the Massachusetts Parental Stress Line at 1-800-632-8188 or find help at www.OneToughJob.org. Anyone who suspects child abuse can call the DCF Child at Risk Hotline at 1-800-792-5200.