The flat head, which has the function of support, is that structure positioned between one carriage and another, which allows the train crew and passengers to pass from one carriage to another. The adjoining heads of two carriages are joined, limited to the central part, by a gusset, which acts as a 'closed central inter-communication'. The cabs are equipped with the flat head as the intercommunicating part towards the rest of the train.

The ceiling and walls are made of leather and shaped like bellows. The floor is formed by two hinged platforms, which are superimposed, but independent, so as to leave the displacement of the heads of the two cars free.