Vehicle cab windscreen air distribution system for a windscreen (1) provided with an external windscreen wiper (5) and a windscreen wiper motor (2a) mounted on the inside of the windscreen. The distribution system comprises an air distribution housing (3) which at least partially surrounds the wiper motor (2, 2a), the housing defining a passage (3a) for the supply of air onto the windscreen (1a) in the vicinity of the motor. The passage (3a) for the supply of air is defined between a motor housing (2) and part of the air distribution housing (3),