Pukka Bundook,
No offense taken! I think, though, the reason the Earl of Southesk chose to illustrate that particular skull is because it was atypical. It is not from a common bison, but from a "buffalo ox." I've run across this term one or two other times in reading the literature of that time. Bear in mind, this was during the Victorian era, and "delicate" topics had to be worded in least offensive terms. The impression I formed was that "ox" was a euphemism for a castrated bull, what I would call a "steer." So, a "buffalo ox" was a castrated male bison, although I could not rule out the possibility of a domestic bull/buffalo cow crossbreed, bearing in mind that the trading posts often kept a few cattle, and I believe it may have been John Palliser who related the story of a particularly randy domestic bull. One traveler speculated the Indians may have occasionally caught bull buffalo calves alive, and castrated and released them, or wolves may have attacked and bitten off the body part under consideration. Anyway, putting it all together, it appears these animals, when compared to ordinary bison, had exceptionally fine robes, larger overall size, and differently shaped horns, which the Earl wanted to illustrate. I can say I once saw, in the Fred Bear Museum, the mounted head of a moose that had grotesquely formed antlers. The docent, a gentleman named Frank Scott and personal friend of Fred Bear, stated that the animal had been castrated early in life. Frank speculated this may have occurred accidentally, when the bull was trying to jump over something and "got 'em caught."
Saskatchewan and the Rocky Mountains is a wonderful book, describing the Earl's extended hunting trip in the mid-19th century, all with muzzle-loaders. I think you can probably search for it and find the entire text online, to read for free. As you live in a part of the world near or through which he traveled, I'm sure it would be of particular interest to you.
Thank you for your comments!
Notchy Bob