The sheep.—The sheep (Fig. 173) differs in several important respects from any of the animals previously mentioned. It is of course a mammal, for it suckles its young, and its body is covered by hair; but the hair is of that warm fleecy kind which is called wool. The fibres of wool are seen under the microscope to be rough and scaly. [Pg 259] For this reason they can be spun into loosely-textured threads which entangle a great deal of air; woollen garments are thus very bad conductors of heat. The wool upon the sheep’s body is slightly greasy, from a substance which is given off by the skin and protects the animal from rain. The toes of the sheep are not armed with ordinary nails or claws, but claws are represented by horny masses called hoofs, which encase the ends of the toes, and upon which the whole weight of the body is thrown. The sheep, especially the male (ram), is often provided with weapons in the form of hollow horns, which grow upon its forehead. Fig. 173.—Sheep. [Pg 260] Fig. 174.—Section of Skull of Sheep. (After Flower.) Fig. 175.—Stomach of a Ruminant opened to show the internal structure. For description, see text. Method of feeding.—The sheep is a strict vegetarian, living largely upon grass. It grips the grass between its lower incisor teeth and a hard pad on the upper jaw; there are no incisor teeth in the upper jaw. Neither upper nor lower jaw bears canine teeth; and the cheek teeth, which are used for chewing the food, have their crowns ridged lengthwise. The arrangement of the teeth of the sheep is shown in Fig. 174. During grazing, however, the food is not at once chewed, but is simply mixed with a large quantity of saliva and swallowed, the chewing-process being performed at a later period. It is obviously a great advantage to an animal, which in the wild state is liable at any moment to be attacked by enemies, to be able to stow away its food quickly, and afterwards masticate it at leisure. This is rendered possible, in oxen, sheep, goats, deer, and the few other animals which chew the cud, by the peculiar form of stomach shown in Fig. 175. The hastily swallowed food is passed into the large paunch b and into the compartment c. When the animal finds an opportunity of “ruminating” or chewing the cud, the food is returned to the mouth in small quantities at a time, and is there finely divided by the cheek teeth. In this condition it is again swallowed, and makes its way at once into the compartment d, where it is strained between leaf-like folds and then passed into the last chamber e, and thence to the intestines, to undergo the final processes of digestion. [Pg 261]