blower 23 of a seat ventilation device 22 and an electric heating coil 26 of a seat heating system 25 the back cushion 14 of the backrest 12 is embodied with a backrest face and two lateral bolsters a cavity 29 which is open at the bottom end of the backrest 12 is provided between the backrest cushion 14 and an air impermeable rear wall 28 arranged in the cavity 29 is a central fan 30 the intake opening 301 of which faces downwards to the open end of the cavity 29 and the delivery opening 302 of which is connected to a flexible duct 31 a heating coil 27 of the seat heating system 25 is arranged upstream of the delivery opening 302 of the fan 13 as in the case of the squab component 11 the back cushion 14 is secured on a cushion carrier not shown here and has a cushion pad 17 a ventilation layer 18 which covers the latter over its entire area a pressure distribution layer 19 which is arranged on the ventilation layer 18 and an air permeable cushion cover 20 which covers the surface of the cushion in the area of the cushion face at the bottom end the ventilation layer.