This is a very old skull from a Stone Age mammal called Ovibos moschatus, as pictured in A monograph of the British pleistocene mammalia, a publication by W. Boyd Dawkins that’s more of an encyclopedia discussing various aurochs, mastodons and other critters who trundled across prehistoric Britain.
Ovibos moschatus is a musk ox.
William Boyd Dawkins was a caver, fossil hunter and an advocate for coal miners’ rights. No idea if he’s related to Richard Dawkins, the evolutionist and gadfly, but his father was also named Richard Dawkins… and a reverend.