The Niagara County Sheriff's Office arrested a Dysinger Road man Friday for assaulting his 5-month-old son.
Christopher Fuller Jr., 23, was charged with first-degree assault and reckless assault of a child after an investigation.
Sheriff's officials say the infant was shaken violently. The infant is listed in critical condition at Buffalo's Women & Children's Hospital.
Fuller was sent to jail after he was arraigned and couldn't make the $25,000 bail.
The Associated Press contributed to this report.