Actually the tear duct is on the inner part of the orbit (where the orbit bone slopes towards the eye). It's difficult to see on a two-dimensional image, but I've enhanced the image below.
In each image, the tear duct is actually the smaller hole (ringed in the lower image) - the larger hole is a nerve opening. In each instance, the duct is positioned just slightly on the inner side of the orbit. The limit of the orbit is indicated with a dotted line in the lower image.
In the image linked to appears to be a cast, and, as such, only shows the larger nerve opening and not the tear duct. Small openings are often missing from casts.
More on monotreme-marsupial-placental evolution soon.
