The popular TodayIFoundOut.com site offers this in-depth, entertaining and mostly-accurate explanation of the generic late-19th century pugilism fighting stance.
The sweeping claim that Victorian boxers held their guards “low” (relative to the modern style) because they preferred to target the body over the face is mildly controversial. Manuals of boxing and written reports on boxing matches during the bare knuckle era consistently demonstrate punches to all legal targets. It’s worth noting that the way pugilists posed for portrait paintings and photographs did not necessarily reflect their actual fighting stances, which in turn depended very much on individual styles, measure and the stances and tactics adopted by their opponents. Also, for the record, “pugilism” should be pronounced with a soft “g”, as in “pew-jill-ism”.