This firing mechanism or gun lock is from a 32 PDR (Pounder) Cannon. The navy locks recovered from the Cairo are the type patented by E. Hidden. The gun lock was designed to ignite the charge by the blow of a piece of metal known as the hammer.
Photograph of the figurehead of the USS Niagara mounted on a large base bearing reliefs of cannon and cannon balls. The figurehead is of a large eagle ready to take flight. Written in lower right is "Figurehead U.S.S. Niagara/ Boston Navy Yard/ May 24, 1902".