Abstract: An internal combustion engine of the "stratified charge" type has for the or each cylinder a primary ignition chamber in the cylinder head which communicates via a throat with its corresponding cylinder. The primary ignition chamber has a generally round concave upper portion, a generally frusto-conical lower side portion and a flat bottom surface towards which the lower side portion tapers. The lower side portion, flat bottom surface and throat are formed in a plug member seated in the cylinder head. The primary ignition chamber has a tapped hole for a sparking plug and an injection hole for a fuel injection nozzle. The throat opens at one end into the primary ignition chamber through the flat bottom surface thereof and runs obliquely to its other end where it communicates with a shallow recess formed in the upper surface of the crown of the piston.