Crankcase ventilation apparatus commonly known as the breather box. This device accepts the oil laden air expelled from your engine while it's running, seperates the oil, routes it back into the crankcase, all while venting the excess air to the atmosphere.
This version was used as original equipment on V7 Sport, 750S, S3, 850T, 850 LeMans and LeMans II. It has the extra two fittings for the vent hoses to the valve covers.
This unit is also commonly used on many later round fin models, such as 850T3, T4, Convert, G5, SP1000 and CX100, when the air filter box is removed and replaced with individual carburetor mounted air filters.