40 Organs of the Animal Body : their Forms and Uses. 
When cut open, the stomachs of all animals show a structure 
which is quite different from the outside. The lining is known 
as mucous membrane, and may be described shortly as an 
altered form of the skin which covers the surface of the body, 
having numerous tubes opening on it from which a quantity of 
fluid (mucus) is constantly flowing. The mucous membrane 
may in fact be called the inside skin which extends from the 
surface of the body, from the mouth all through the swallow,, 
the stomach and intestines, and through the nostrils, through 
the windpipe and all the breathing-tubes. 
Fig. 26. — Stomach of the Horse. 
A. Portion of swallow ; B. Comracncciuent of small intestine. 
If the carcass which is under examination is that of an 
ox or sheep, the stomach will present the appearance seen in 
Fig. 27. 
The chief compartment of the stomach in the ox and sheep 
(rumen) occupies a large part of the cavity of the abdomen ; 
indeed, very little else can be seen until the stomach is removed, 
A small compartment in front of the paunch, the reticulum, is 
distinguished by the peculiar honeycomb form of its lining 
