Abstract: A timepiece movement movement comprises a casing having a mechanical energy source, a work train driven by the energy source, a fixed wheel mounted on the casing, and a tourbillion comprising a cage which bears a balance wheel, an escape mobile provided with a pinion engaging with the fixed wheel, and a cage wheel rotationally joined to the cage and provided on its periphery with a toothing engaging with the work train. The casing of this movement is constituted, in its part occupied by the tourbillion, by a transparent material. In addition, the cage wheel comprises a transparent-material platelet, which extends radially beyond the other constituents of the tourbillion.