3

"[…] Book III, which deals with the arrangements of temples and the ionic order (or genus, pl. genera which is the term used by Vitruvius)"

Comment:
Does the author really think readers interested in this topic would not know that Vitruvius speaks of "genus" and that its plural is "genera"?

"… and in Book IV where the subject is the Doric and Corinthian orders."

Comment:
Better: "… where the subjects are the Doric and Corinthian orders" ?

"When relating the drawings to what Vitruvius writes in the passage next to the illustrations it can be noticed, that although Vitruvius mentions the column as an im- portant element – the element from which the bases take their proportions – Giovanni Battista barely sug- gests the columns and the relation between column and base."

Comment: The reason could and should be, that this relation – or rather the usage of the column's shaft as the basic module for the other parts – would be a very common part of the basic knowledge of an architect trained in Italy around 1500. So, there would be no need to notice or comment on topics like that – as we would still do today in our annotations to texts: We do not note the obvious, but those parts, we are more interested in because they are not obvious to us. So, I would not see this lackage of the column as an opposition to the following as the beginning of the next sentence with the word "instead" suggests, but rather as a sign of what is already known to Giovanni Antonio and was is rather new or requires a drawing to make it better understandable (to him or others).