[Edgar Bergen]
Origins A Short Etymological Dictionary of Modern English:
hogshead (a hog's head, prob from shape)
Etymological Dictionary of the English Language:
HOGSHEAD, ... Certainly derived from ME. hogges hed, "hog's head" [duh]; a fanciful name, of which the origin is not known; ... Hence were borrowed MDan. hogshoved, a hog's head, modified into Dan. oxehoved, as if it meant "ox-head;" Low G. hukeshovet, a hogshead (Lubben); also Swed. oxhufvud, a hogshead, lit. "ox-head;" G. oxhoft, a hogshead; Du. oxhooft.'
and Horsefeathers & Other Curious Words, Charles Funk:
hogshead For six hundred years, at least, this measure of liquid capacity has been in our language (and taken into other Teutonic languages, with hog sometimes changed to bull or ox), but as yet the mystery of its source or a plausible reason for the name remains unsolved. One guess, quoted by the learned W.W. Skeat, is that the earliest cooper of these casks of two-barrel size branded his product with the outlines of the head of a hog or of an ox. But Skeat also says that most of the conjectural sources are "silly." And I have nothing to add to that.
[/Edgar Bergan]
