62 
THE VETERINARY SCIENCE 
burying ground of the red corpuscles. It is well supplied 
with blood vessels and nerves and weighs in the average 
horse from two to four pounds. 
III. — MEMBRANES OF THE BODY. 
Membranes of the body are spoken of as Mucous or 
Serous. 
11. Mucous Membrane. — All open cavities of the body 
are lined with mucous membranes, as, for example, the lining 
all through the alimentary canal of the digestive organs. The 
lining of the respiratory or breathing organs is of mucous 
membrane, as also is that of the urinary and genital organs 
or those which produce the young animals. 
12. Serous Membranes form the lining of closed cavities, 
that is air-tight cavities, those that do not communicate at all 
with the air. The peritoneum, situated between the bowels 
and the wall of the abdomen, is an important example. The 
pleura which lines the chest cavity and the lungs is another. 
A third, less important, may be found in the brain. 
Serous membrane is always made up of two coats, the 
inner being attached to the organs contained in the cavity 
and the outer closely lining the inside of the cavity in which 
it is found. An oily fluid is always secreted from the inner 
side of these membranes. This fluid lubricates the surfaces, 
and thus prevents soreness or inflammation that would other- 
wise result from the friction caused by the moving of one 
coat on the other. These membranes are very important and 
should be very carefully noted, as they sometimes become 
chilled and inflamed and thus the source of further inflam- 
mation. Inflammation of the pleura is called pleurisy. In- 
flammation of the peritoneum, the membrane connected with 
the bowels, is called peritonitis. It is a very dangerous dis- 
ease, much more so than pleurisy. 
IV. — ^THE PROCESS OF DIGESTION. 
The food is taken into the mouth by the lips and front 
teeth. Here it is masticated or chewed by the teeth with 
the assistance of the tongue, at the same time receiving from 
the salivary glands a digestive fluid called the saliva which 
softens and prepares it for digestion. After being thoroughly 
ground up and mixed with saliva it is rolled into a ball at 
the back part of the tongue, where by the action of the 
