Apple iBook Reader Lacks "Go Back" Button

Since Seton Hill is giving iPads to all full-time students, I have been looking at the comparative features of several eBook readers.
Right now, the Kindle app for the iPad looks good, because it offers notes and highlighting, but it lacks an iintegrated pop-up dictionary, which severely hurts is usefulness to student readers.
I like the iBook’s dictionary and its ability to highlight in different colors; the update that was pushed out today does permit annotations, which is a great improvement, and for a while made me put the iBook reader first on my list.
I tried out one of Penguin’s enriched ebooks, which features classic texts with helpful hypertext notes. Unfortunately, I can’t seem to find any way for the iBook to “go back” to the previously viewed page. When they hyperlinks are bidirectional, as they are in case of the illustrations in my eText of Huck Finn, but the footnotes are not bidirectional — there is only a link from the main text to the footnote, but the page of footnotes does not include a link to take the reader back to the main text.
While Penguin should probably have considered the questionable value of one-way hyperlinks, the “go back” button is such an important part of the online experience that I’m surprised not to find it in the iBook.