The external characters of the rabbit.—The outside of the rabbit’s body is almost entirely covered with fur. This consists of two kinds of hair—coarse and fine. The coarser hairs are fewer in number and longer than the fine ones, which they protect from wet. The fine hairs are extremely closely-set, and stand straight out from the skin. In a seal-skin coat only the short hairs of the fur are to be found; the longer hairs have been removed by the dressing process. The great warmth of furs is due to the air which is entangled between the fine, close hairs. It is generally the case that fur-bearing animals are exposed to either mud or wet by their method of life; in spite of this fact, while the hair of a dog soon becomes wetted by rain, and the wool of a sheep retains a great deal of dirt, furred animals are noted for keeping their coats clean and dry.
The longest hairs of the rabbit are the stiff whiskers which stand out from the upper lip, the cheeks, and above the eyes. They are extremely sensitive to touch, and are of great assistance to the animal in finding its way through the dark burrows.
The colour of the wild rabbit is greyish brown, except on the belly and under the tail, where it is white. This colour harmonises well with the surroundings, and renders the animal much less noticeable. Wild rabbits are exposed to so many enemies, that individuals which happen to be born with conspicuously coloured fur have generally but a poor chance of surviving and leaving offspring to inherit their disadvantages. There is thus in each generation a natural selection of the animals which are best protected, by their colour, from observation. Among tame rabbits, on the other hand, protective colouration is of very little importance, and one variation of colour is as likely as another to be transmitted by heredity to the next generation.
The regions of the body.—For convenience and precision in describing animals it is customary to use the words anterior and posterior to indicate the fore, or head, end, and the hind, or tail, end respectively. The belly-surface is said to be ventral, and the back dorsal.
The body of a rabbit obviously consists of head, trunk, a short tail, and four limbs. The general arrangement of the bony framework, or skeleton, ([Fig. 161]) which supports the softer parts may be felt through the skin. The skeleton consists of (1) the skull; (2) the spine or vertebral column (generally spoken of as the backbone), placed dorsally, and reaching from the anterior end of the neck into the tail; (3) the ventral sternum or breast-bone, which is connected with the vertebral column by means of curved ribs; (4) the bones of the two pairs of limbs, with the shoulder-and hip-bones to which they are attached. The bones will be studied in more detail in the next chapter.
The trunk is divided into two regions—an anterior thorax, or chest, (enclosed in the bony cage formed by the ribs, sternum, and the adjoining part of the vertebral column), and a posterior abdomen. The two cavities are divided from each other by a fleshy partition called the diaphragm.
Organs of special sense.—In addition to the sense of touch which is possessed by the whole surface of the body, the rabbit has organs which enable it to distinguish objects by sight, sounds, scents, and taste. Its sense of smell is so keen that, to be successful in snaring rabbits, “in walking to the spot selected for the snare it is best to avoid even stepping on the run, and while setting it up to stand back as far as convenient and lean forward. The grass that grows near must not be touched by the hand, which seems to impart a very strong scent. The stick that has been carried in the hand must not be allowed to fall across the run; and be careful that your handkerchief does not drop out of your pocket on or near it. If a bunch of grass grows very tall and requires parting, part it with the end (not the handle) of your stick.”[8]
The shape of the ear-flaps, which can be turned in different directions ([Fig. 159]), enables the rabbit to catch very slight sounds.
The eyes are placed on the sides of the head, so that the animal has a wide field of view, and an enemy approaching from behind is not likely to be unnoticed. The eye of the rabbit is very similar in structure to our own, but it possesses one useful adjunct which ours has lost, in the shape of a third eyelid—an opaque flap of skin which lies in the inner angle, and can be drawn over the eyeball at will. The little fleshy nodule in the corresponding position of the human eye is a rudiment of a similar structure.
The rabbit a gnawing animal.—Rabbits are much addicted to gnawing young trees for the sake of the bark and the softer juicy tissues between bark and wood. Even tame rabbits exhibit the same instinct by gnawing their wooden hutches, although these are of no use as food. The gnawing is done by the sharp teeth, called incisors, which are conspicuous in the middle of both upper and lower jaw. In the upper jaw two incisors (which are so deeply grooved that they look like four) are visible even when the mouth is closed, owing to the split in the middle of the upper lip. The hardest part of the tooth (a substance called enamel) is at the front. Behind this the tooth is composed of a softer, bony material called dentine; and the back of the tooth consists of still softer dentine. The result of these differences in the composition of the various parts of the tooth is that the gnawing of hard substances wears away the back of the tooth most, the middle part next, and the front least of all; and thus a sharp chisel-edge is always maintained. Moreover, the teeth of the rabbit never stop growing, so that they never become appreciably shorter through use. Immediately behind the two visible incisors of the upper jaw, another and smaller pair can be felt by the finger; the enamel-faces of these are directed backwards towards the cavity of the mouth. The softer and more easily worn faces of the two pairs of upper incisors are thus in contact, and are continually worn down to form a groove. Into this groove the two incisors of the lower jaw bite. The incisor teeth stand well out from the jaws, and the split upper lip can be drawn back, so that the lips are not injured by gnawing. In the hinder part of the mouth, where the chewing, or mastication, of the food takes place, are six flatter but cross-ridged grinding teeth on each side of the upper jaw, and five on each side of the lower jaw. The insides of the cheeks are protected from sharp splinters of wood by a patch of hair on each side, which extends from the region of the incisors to the grinding teeth behind. The roof of the mouth is protected by hard cross-ridges, and the tongue by tough skin.