Complex sentence: Gross anatomy traditionally divided the liver into two--a right and a left lobe, as viewed from the front (diaphragmatic) surface; but the underside (the visceral surface) shows it to be divided into four lobes and includes the caudate and quadrate lobes.
Split into simpler sentences: Gross anatomy traditionally divides the liver into two--a right and a left lobe, as viewed from the front (diaphragmatic) surface. However, when viewed from the underside (the visceral surface) it can be divided into four lobes: the right lobe, the left lobe, the caudate and the quadrate lobes.