Cylinder head of an internal combustion engine

An engine is provided with a cylinder head defining a coolant jacket therein that is formed from a series of passages interconnected by a series of curved junctions to direct coolant about spark plugs, exhaust valves, and an integrated exhaust manifold in the head. The cooling jacket has a first longitudinal passage with an annular section about a spark plug, a second longitudinal passage with an annular section about an exhaust valve, and a third passage surrounding an integrated exhaust manifold and fluidly connecting the first and second passages. The first passage has a continuously decreasing area and the second passage has a continuously increasing area in a direction of coolant flow.