Lubrication structure for internal combustion engine

A lubrication structure for an internal combustion engine, the internal combustion engine including a crankcase divided into a left crankcase and a right crankcase along a longitudinal centerline, and having a crankshaft arranged transversely therein, said lubrication structure comprising:

• an oil pump having a pump chamber provided at a first end of an oil pump shaft, said oil pump shaft arranged in parallel with the crankshaft;
• a plurality of oil passageways extending from a side surface of the pump chamber of the oil pump to a second end of the oil pump shaft, said oil passageways arranged in parallel with the oil pump shaft;
• an oil filter positioned facing towards the oil passageways;
• an oil introduction passageway extending vertically from a first oil passageway to the oil filter;
• and
• an oil discharge port forming an oil supply passageway from an oil pan positioned in a lower portion of said crankcase.