The piece is not Civil War ---- Civil War pistols were Black Powder and would require a LOADING LEVEL , which yours lacks
What you have there is some sort of TOP BREAK pistol 1880's - mid 1920"S
There is a latch on top just above where the HAMMER would be on a regular pistol , If you lifted the latch the barrel assembly would pivot on a pin ( directly infront of the trigger guard causing the weapon to break in half
S&W were the primary manufactures ( but other companies also made similar models The S&W were nicknamed The Lemon Squeeze