Abstract: A casing structure for an annular combustion chamber of a turbojet engine is disclosed in which air is tapped from an upstream end portion of the casing, while at the same time preventing contamination of such tapped air from the injected fuel. The casing has annular inner and outer walls disposed on either side of the combustion chamber. The casing has an upstream end which is attached to the downstream end of the exhaust gas turbine. The outer annular casing wall defines circumferentially spaced apart fuel injector orifices and circumferentially spaced apart air tapping orifices which are circumferentially alternating with the fuel injector orifices. A partition wall extending between an air diffuser and the inner surface of the outer annular wall divides the radial space separating the diffuser and the outer annular wall into first cavities which communicate with the air tapping orifices and second cavities which communicate with the interior space between the inner and outer annular walls.