The front case is an aluminum case that contains the oil pump and bolts as a whole to the timing side of the engine. There are various seals that reside in the front case. The front main seal where the crank protrudes through the case as well as the oil pump seal. There is also a gasket between the front case and engine. The oil filter housing also bolts to the front case, in the bottom left in the picture.
When using balance shafts, the front balance shaft is connected to the front case. The rear balance shaft goes through the front case and is held on by the oil pump/oil pump sprocket. The oil pump bolts to the inside of the front case.