That line drawing is short on detail depth. Things we would like to see we can't. If it is an illustration I wouldn't give it much credence as representative of correct detail. If it is a drawing, then there may be additional detail. It is plate one, perhaps plate two shows additional detail.
Wikipedia credits the drawing from Vaisseau de Ligne, Time Life, 1979. Need to get a copy of that book. WWW.ABEbooks.com list the book in French. Vaisseau de Ligne translates to Ship of the lines, but I don't find an English language Time-Life book by that name. There is a Time-Life book called Fighting Sails.
If some body has a copy of that book, can you look for that illustration and tell us it's source?
It would be interesting to see another angle. Other than a couple of carronades I found on field carriages and garrison carriages, I haven't seen any other Carronade mount that didn't have pivot point and opposing traverse. The all have thissimilar mountings.
It wouldn't make sense to have such a rigid mount, as there would be no way other than changing direction of the ship to aim. Not realistic at all.