When I first read the sentence in blue bracket, I subconsciously regard "with rows of smaller ridges" as a modifier of "spines". Now I realize that it makes more sense to think it modifying "ridges." So is it more reasonable to put the modifier closely after the thing being elaborated, so it'll not confuse people?
X is like Y.
All of Y is describing X by analogy. In that sense, Y as a whole is modifying our conception of X.
Imagine the skeleton of the human trunk between the hips and shoulders. What do you see? A spine and ribs. But the ribs themselves do not connect to each other; rather each connects separately to the spine. Now imagine that the ribs have little spurs.
You must apply the entire picture to the ridges as an approximation.