As all development in the history of small guns seems to derive from large cannons/artillery pieces, here is the predecessor of the above posted haquebuts with long tillers: a piece of artillery, illustrated in a Swiss Gothic manuscript (codex), on the adventures of the first crusade, preserved in the Stiftsbibliothek St. Gallen, Cod.Sang. 658, fo. 61, detail.
Please also note the tiller arquebus fired by a soldier in the second close-up.
As this profusely illumniated book, hitherto virtually unknown, offers vast and manifold sources on 15th century weapons of all kinds, here is the link for download:
http://www.e-codices.unifr.ch/de/preview/csg/0658
Best,
Michael