I have a lovely old book from England that was given to me for my first Christmas by my godmother, for future reference. It's entitled "Christmas" by Christina Hole. She says:

"...Chief over all, the boar's head.
This ...has a long lineage. It was eaten during the Scandinavian Yule in honor of the Sun-Boar. The heroes of Valhalla were believed to feast continually on boar's flesh, and the animal itself was sacred to Celt and Norseman alike. At the great medieval Christmas banquets the head was garlanded with rosemary and bay, and an orange or an apple was thrust between its teeth. It was brought in with ceremony to the sound of trumpets, slowly borne in upon a gold or silver dish by the chief cook, and accompanied by a procession of minstrels and servants. This custom is still observed at the Queen's College, Oxford, where the decorated head is carried on a silver basin by four men, preceded by the chief singer, and followed by a choir singing the refrain of the ancient Boar's Head Carol. Three times the procession halts, while a verse of the carol is sung by the chief singer, and finally the head is placed upon the high table, where the orange from its mouth is presented to the chief singer, and the sprigs of rosemary and bay are distributed amongst the guests."

The book gives no date, but her bibliography includes books published in 1954, so it was sometime between 54 and 1960 (my first Christmas!). My godmother's name, by the way, was Rosemary!