It is a improved Anson system or Anson system with upper rods which was designed by Ernst Kerner. The scear is hinged by the top screw at the back of the frame and it mates to the top of the hammer. Note the pin at the lower position of the back of the receiver which holds the mainspring at the back of the hammer which is held by the shaft that has the cocking indicator on the end.

Kind Regards,

Raimey
rse