The paunch is lined with a thick membrane, presenting numerous prominent and hard papillæ. The inner surface of the second cavity is very artificially divided into angular cells, giving it somewhat the appearance of honeycomb, whence its name "honeycomb-bag." The lining membrane of the third cavity forms numerous deep folds, lying upon each other like the leaves of a book, and beset with small hard tubercles. These folds vary in breadth in a regular alternate order, a narrow fold being placed between each of the broader ones. The fourth cavity is lined with a velvety mucous membrane disposed in longitudinal folds. It is this part of the stomach that furnishes the gastric juice, and, consequently, it is in this cavity that the proper digestion of the food takes place; it is here, also, that the milk taken by the calf is coagulated. The reed or fourth cavity of the calf's stomach retains its power of coagulating milk even after it has been taken from the animal. We have a familiar instance of its operation in the formation of curds and whey.
The first and second cavities (a and b) are placed parallel (or on a level) with each other; and the œsophagus (e) opens, almost equally, into them both. On each side of the termination of the œsophagus there is a muscular ridge projecting, so that the two together form a sort of groove or channel, which opens almost equally into the second and third cavities (b and c).
[As there has not been, as far as I am aware, any appropriate name given to this very remarkable part of the stomach of ruminants, I here take the liberty of suggesting the term Gastro-duct, by which epithet this muscular channel will be designated in the following pages.]
View of Gastro-duct, after Flourens.
a. A portion of the œsophagus cut open, showing the internal folds of the mucous membrane.
b. The opening of the œsophagus into the paunch.
c, c. The gastro-duct.
d, d. Muscular fibres passing completely round the edge of the gastro-duct, and forming a sort of sphincter.
e. The opening from the gastro-duct into the third cavity.
All these parts, namely, the œsophagus, the gastro-duct, and the first three cavities, not only communicate with each other, but they communicate by one common point, and that point is the gastro-duct. At the extremity of the third cavity, opposite to that at which the gastro-duct enters it, is an aperture which communicates immediately with the fourth cavity (d).
Such is a very brief description of the complicated stomach of the Ox Tribe. In what manner the food passes through this curious arrangement of cavities is a problem which has engaged the attention of naturalists from a very early period. A host of great men might be cited who have failed to solve it. The French physiologist, M. Flourens, by his recent experiments, has done more than any or all of his predecessors to give clearness and precision to this intricate subject.
The following is an abstract of the most important of his experiments:—
A sheep having been fed on fresh trefoil, was killed and opened immediately,—that is, before the process of rumination had commenced. He (M. Flourens) found the greatest part of this herb (easily recognised by its leaves, which were still almost entire,) in the paunch; but he also found a certain portion (une partie notable) of those leaves (in the same unmasticated state) in the honeycomb. In the other two cavities, (the many-plies and the reed,) there was absolutely none.