precise. An alternative explanation is that of George E. Nunn (see below). Chet Van Duzer has said that the explanation for the depiction of the Ocean to the west of America is that Marco Polo had stated that Zipangu (Japan) was an island, so that there had to be sea between it and America, which Waldseemüller had concluded was also an island. Mundus Novus, a book attributed to Vespucci (who had himself explored the extensive eastern coast of South America), was widely published throughout Europe after 1504, including a version by Waldseemüller's group in 1507 under the title, Quatuor Americi Vespucii Navigationes. It expressed the belief of Vespucci and his companions that: "We knew that land to be not an island but continent, both from its long extending coasts which do not enclose it and from the infinite number of inhabitants which it contains". "Continent" meant, at that time, one of the three known continents, Europe, Africa and Asia, that adjoined each other (from Latin "continens"="touching") surrounded by the Ocean, which was divided by Africa into the Western, or Atlantic and Eastern, or Indian Oceans which contained the Earth's large and small islands. Vespucci's belief, therefore, was that the land was part of the continent of Asia. It has been theorized that "continent" in the Mundus Novus meant the same as its modern meaning, that is, one of the Earth's main continuous land-masses, and that therefore it had first introduced to Europeans the idea that this was a new continent and not Asia, and that this led to Waldseemüller's separating the Americas from Asia, depicting the Pacific Ocean, and the use of the first name of Vespucci on his map. An explanatory text, the Cosmographiae Introductio, widely believed to have been written by Waldseemüller's colleague Matthias Ringmann, accompanied the map. It was said in Chapter IX of that text that the Earth was now known to be divided into four parts, of which Europe, Asia and Africa, being contiguous with each other, were one continent, while the fourth part, America, was "an island, inasmuch as it is found to be surrounded on all sides by the seas". This differed from the belief expressed by Vespucci in Quatuor Americi Vespucii Navigationes, published in the same book as an appendix, that the land he found was part of the continent of Asia: "After nineteen days we reached new land, which we took