This chewing the cud is a phenomenon restricted to the group of animals now under consideration, although it may be mentioned that some naturalists have thought that the Kangaroos among the Marsupials do the same to a certain extent.
As to the details of the process, the individual, a Cow, for instance, whilst grazing, nips off the grass between the large cutting teeth in the front of the lower jaw, and the tough pad which replaces in these creatures the similarly situated teeth of the upper jaw. After each mouthful it does not proceed to masticate the food, but swallows it forthwith, and continues thus to graze until it has satisfied its appetite. Seeking a quiet and shaded spot, it then seats itself that it may ruminate, or chew the cud, at leisure. If watched it will be seen that it commences shortly to perform a slight hiccough action, in which some contraction of the flanks is to be noticed. Its mouth, which was previously empty, is found to be full of what it is not difficult to recognise to be coarsely-masticated grass, which has been forced up into it; and this it immediately proceeds to chew between its back or grinding teeth, in a slow and continuous manner, moving its lower jaw uniformly from one side to the other—from right to left. When this chewing process has lasted for a time sufficient to convert the food into a pulpy state, it is again swallowed, after which another bolus is brought up to undergo a similar operation. And this is repeated at frequent intervals until most of the food swallowed has been masticated.
A complicated stomach is necessary for the operation of this elaborate chewing process, the undisturbed duration of which has led to the word by which it is designated being applied metaphorically to a brooding condition of mind. Thus the poet of the “Night Thoughts” says:—
STOMACH OF A RUMINATING ANIMAL: (A) EXTERIOR, (B) INTERIOR.
“As when the traveller, a long day past
In painful search of what he cannot find,
At night’s approach, content with the next cot,
There ruminates awhile his labour lost.”