Abstract: Device for the ventilation of a transmission case (11) that is normally intended to hold liquid lubricant for transmission components and includes a residual internal volume of air inside the transmission case that is connected to the atmospheric pressure by way of a passage. With the aim of reducing the quantity of dirt particles than can get into the transmission case by way of the said passage, the passage includes a first section (27) with a certain flow area and a second section (26) with, by comparison, an at least approximately 50% larger flow area. The first section (27) is situated between the atmosphere and the second section (26). A compressed air source (18) is connected to the passage between the internal volume of the transmission case (11) and the first section (27).