The Book of Household Management by Mrs. Beeton

it lives, the more difficult is the process of assimilation, and the more complex the chain of digestive organs; for it must be evident to all, that the same apparatus that converts _flesh_ into _flesh_, is hardly calculated to transmute _grass_ into flesh. As the process of digestion in carnivorous animals is extremely simple, these organs are found to be remarkably short, seldom exceeding the length of the animal's body; while, where digestion is more difficult, from the unassimilating nature of the aliment, as in the ruminant order, the alimentary canal, as is the case with the sheep, is _twenty-seven times the length of the body._ The digestive organ in all ruminant animals consists of _four stomachs_, or, rather, a capacious pouch, divided by doorways and valves into four compartments, called, in their order of position, the Paunch, the Reticulum, the Omasum, and the Abomasum. When the sheep nibbles the grass, and is ignorantly supposed to be eating, he is, in fact, only preparing the raw material of his meal, in reality only mowing the pasture, which, as he collects, is swallowed instantly, passing into the first receptacle, the _paunch_, where it is surrounded by a quantity of warm saliva, in which the herbage undergoes a process of maceration or softening, till the animal having filled this compartment, the contents pass through a valve into the second or smaller bag,--the _reticulum_, where, having again filled the paunch with a reserve, the sheep lies down and commences that singular process of chewing the cud, or, in other words, masticating the food he has collected. By the operation of a certain set of muscles, a small quantity of this softened food from the _reticulum_, or second bag, is passed into the mouth, which it now becomes the pleasure of the sheep to grind under his molar teeth into a soft smooth pulp, the operation being further assisted by a flow of saliva, answering the double purpose of increasing the flavour of the aliment and promoting the solvency of the mass. Having completely comminuted and blended this mouthful, it is swallowed a second time; but instead of returning to the paunch or reticulum, it passes through another valve into a side cavity,--the _omasum_, where, after a maceration in more saliva for some hours, it glides by the same contrivance into the fourth pouch,--the _abomasum_, an apartment in all respects analogous to the ordinary stomach of animals, and where the process of digestion, begun and carried on in the previous three, is here consummated, and the nutrient principle, by means of the bile, eliminated from the digested aliment. Such is the process of digestion in sheep and oxen.