Both of these gentlemen have provided me their insight on this topic as well as sources. This would have been impossible to complete without them. They authored this work as much as I did and reviewed and offered suggestions and comments along the way.
Footnotes appear at the end of each section.
Added link to other research on land transport. Spelling errors in harness.html, dorsal.html corrected. Books by Langdon and Treue added to bibliography. Spelling corrections in horse. Two new bibliography items.