Meaning of ‘snakes downwards and then onwards, in three columns, for another four pages’

The passage below is from A History of the Index by Dennis Duncan.

Grosseteste’s index survives now in a single, incomplete copy, a manuscript kept in the municipal library at Lyon in south-eastern France. A title in red ink announces, ‘Here begins the table of Master Robert, Bishop of Lincoln, with the help of Brother Adam Marsh.’ Beneath it, a column of glyphs – dots, squiggles, geometric shapes, tiny illustrations, a sun, a flower – snakes downwards and then onwards, in three columns, for another four pages. Each sign is accompanied by a concept: eternity, imagination, truth … These are the topics, or subjects, of Grosseteste’s index. Unlike the alphabetically arranged distinctiones of Peter the Chanter, Grosseteste’s Tabula is ordered conceptually. The topics, all 440 of them, are grouped into nine top-level categories, broader themes like the mind, created things, the holy scriptures. So, taking Grosseteste’s first category, God, as an example, it is broken down into thirty-six topics: that God exists, what God is, the unity of God, the trinity of God, and so on.

My problem is that I cannot visualize the underlined phrase. Of course I cannot explain in any logical way to this graphical description. I think the problematic word is ‘onwards’. It’s definition in dictionary reads ‘Moving or tending forward’. But that didn’t help me. ‘Moving forward’ can point any direction according to the viewer’s perspective. So I drew, though somewhat cursory, a picture for that phrase with two options. One above shows ‘onwards’ in breathwise ‘for another four pages’ and the other one below shows ‘onwards’ in lengthwise for the same pages. Can you tell me which one suits the phrase?

Thanks in advance.