Backrests of a rear seat system are attached to a cross member which extends between the wheel housings of the rear structure of a motor vehicle. Owing to this indirect attachment of the backrests, instead of a direct attachment to the rear structure, the intermediately connected cross member is in a position to absorb a large part of the impact force to which the backrests are exposed in a rear-end collision, and to dissipate this force by means of a parallelogram-like deformation. As a result, the rearward displacement of the backrests is reduced, thus improving the interior protection of the occupants.