I found this very interesting image at 2ch that shows in a quite extreme way the evolution of the drawing style of manga since the Edo era (last frame) until nowadays (first frame). The frame of the Edo era is not really manga but you can already see the fundamentals of what the style would be a century later in Japanese manga. The most exaggerated frame is the second one, belonging to the 90s, the golden era of shōjo manga, like for example Sailor Moon. The third one corresponds to the Dragon Ball years, and the fourth and fifth have an Osamu Tezuka and Tetsuya Chiba (Ashita no Joe) feel. On the other hand the first frame corresponds to the manga style mostly used in the last decade, maybe the most neuter and boring one.