complicated organs, the reader is referred to the
interesting work on 'Cattle,' by W. Youatt.

The paunch is lined with a thick membrane, presenting numerous prominent
and hard papillae. 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 oesophagus (_e_) opens, almost
equally, into them both. On each side of the termination of the
oesophagus 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.]

[Illustration: View of Gastro-duct, after Flourens.

_a._ A portion of the oesophagus cut open, showing the internal folds
of the mucous membrane.

_b._ The opening of the oesophagus 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 oesophagus, 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