RUMINANTS' STOMACHS cause me a great deal of linguistic anxiety. If you look up omasum in Chambers Dictionary, you will find it means "a ruminant's third stomach, the psalterium or manyplies". Look up psalterium and you will find it is the omasum or manyplies, while the entry for manyplies tells us it or they (for the word is sing. or pl.) is or are the omasum or psalterium.
So far, so good, but what about the fardel-bag? A fardel is "anything cumbersome or irksome; the third stomach of a ruminant, the manyplies or omasum". No mention of the psalterium though. And a fardel-bag is defined only as "the omasum".
Having so many words for the third stomach of a ruminant is all rather cumbersome and irksome. Quite a fardel, in fact.