Rumination, or Chewing the Cud.—Food when first taken into the mouth of a ruminant is but lightly masticated and mixed with the saliva from the salivary glands, after which it is swallowed, passing through the oesophagus into the rumen or paunch (first stomach). This division acts as a reservoir or storehouse for food thus eaten quickly. When the animal has time, so to speak, he lies down or stands quietly and completes the process of mastication of his food by chewing the cud. This peculiar act is performed as follows: After being softened and moistened by warmth, the food passes from the rumen or paunch into the second division—the reticulum, honey comb or second stomach. In this small globe-like compartment the food is moistened and compressed into pellets—the cud. By a peculiar reverse action of the oesophagus or gullet these pellets are taken back into the mouth for further mastication or chewing. When re-mastication is completed it is again swallowed, but this time it passes directly into the omasum, many-plies or third stomach, and thence to the fourth or true stomach.
Process of Digestion After Rumination.—Following rumination which, strictly speaking, is the first step in the digesting process, the food passes into the third stomach. The fine parts pass right along to the fourth stomach while the coarser parts are drawn between the folds of the membrane in this division and worked about until it is fine and ready to pass into the fourth stomach, where it becomes fully digested by the action of acids and gastric juices which are secreted in this part. It then passes into the small bowels, and is acted upon by the bile from the liver and the pancreatic juice from the pancreas. These juices are emptied into the first part of the small bowels through little ducts or tubes, which lead from the glands down to the bowels, just on the same principle as that of the horse. After this, throughout the rest of the bowels, the nourishment of the food is taken into the system by means of little glands which are situated in the coating of the bowels. The nourishment when once in the blood goes to supply the different parts of the body, while the part containing no nourishment or undigested passes off through the back bowels in the form of feces.
TEETH.
Teeth are objects situated in the upper and lower jaws. They are made of the same tissues as bone but contain 101⁄2 per cent. more of earthy salts. This fact accounts for their extreme hardness. Unlike bone they can stand exposure to air and friction without becoming diseased. Teeth are used to masticate or chew the food, and because of the constant change in their formation and appearance they serve as a guide in telling the age of the horse.
There are three hard structures that enter into the formation of the teeth—Dentine or Ivory, Enamel, and Cementum, or Crusta Petrosa.
The Dentine, or ivory, is situated in the upper part around the pulp or nerve cavity. It is of yellowish color and largely supplied with nerves which pass through it from the pulp cavity.
The Enamel is the hardest substance of the tooth, and covers the outside of all the exposed part. This substance is characterized by its whiteness and, unlike the dentine, contains no blood vessels or nerves. If part of the enamel is broken off it is never replaced, and the tooth below the broken part generally becomes decayed.
The Cementum, or crusta petrosa, is found in the fang or root and the parts situated below the gum. It is the softest part of the tooth.
Teeth may be simple or compound. Simple as in the dog, where the entire exposed surface is covered by a solid cap of enamel, which alone is in wear; compound or complex, as in the horse, where various tissues are in wear. A tooth consists of the following anatomical parts: The body, or crown, that part above the gum; the table, the part that comes into wear on the top; the neck, the part to which the gums are attached; and the fangs or roots, the parts situated down in the bone.