HEDGEHOG (Erinaceus europaeus, Linn.), the Common Urchin of Pennant, Hérisson of the French, Riccio of the Italians, Igel of the Germans, is the best known, and from an anatomical point of view perhaps the most charac-teristic, of the Insectívora. The genus is remarkable for its dentition, its armature of spines, and its short tail, while the ordinary species is characterized by not having the spines longer than the head or the ears more than half that length. The upper jaw is longer than the lower one, and the whole snout, which is long and flexible, has somewhat the appear-ance of that of the hog; the nostrils are narrow; and the claws are long but weak. The animal is about 10 inches long, its eyes are small, and the integument of the ventral surface is covered with hairs of the ordinary character. The brain is remarkable for its low degree of development, the cerebral hemispheres being excessively small, and marked with but one groove, and that a shallow one, on each side, while the more special characters of this region call to mind the organization of the same parts in the very lowest of mammals.
The most remarkable point in its external appearance is the possession of spines, and the power possessed by it of rolling itself up into a ball, from which these spines stand out in every direction. The spines, which are modified hairs, are sharp, hard, and elastic, and form so efficient a defence that there are but few animals that are able, and even they rarely, to effect a successful attack on this curious creature. The moment it is touched, or even hears the sound of so alight a menace as the report of a gun, it rolls itself up by the action of the powerful muscles which lie just beneath the skin, while this same contraction effects the erection of the spines. The most important muscle is the orbicularis panniculi, which extends over the anterior region of the skull, as far down the body as the ventral or purely hairy region, and on to the tail; three other muscles are connected with this, and aid in the contraction of the integument, passing as they do from the breast-bone to the face and lower jaw, from the fore-arm to the sides of the ventral region, and from the fore-arm to the dorsal surface.
Though insectivorous, the hedgehog is reported to have a great liking for mice, while frogs and toads, as well as plants and fruits, all seem to be acceptable; its ingestion of snakes has been detailed by Buckland and Broderip, and its fondness for eggs has caused it to meet with the enmity of game-preservers. Pennant reports that " it lies under the undeserved reproach of sucking cattle, and hurting their udders, but the smallness of its mouth renders that impos-sible," nor does it seem that any well-authenticated report of such an occurrence has ever been made. It makes a not rare domestic pet. In a state of nature it does not emerge from its retreat during full daylight, unless urged out by hunger or by the necessities of its young. During the cold of winter it passes into a state of complete hiberna-tion, and its temperature falls very considerably; having provided itself with a nest of dry leaves, it is well protected from the influences of the rain, and rolling itself up it re-mains undisturbed till distinctly warmer weather returns. In July or August the female brings forth four to eight young, or, according to others (Bell), two to four at a some-what earlier period ; at birth the spines, which in the adult are black in the middle, are white and soft, but soon harden, though they do not attain their full size until the succeed-ing spring. It is commonly found in woods and gardens, and extends over nearly the whole of Europe ; it has been found at 6000 to 8000 feet above the level of the sea. The witch in Macbeth who heard the "hedge-pig" whine thrice and once gave not an incorrect account of the character of its voice, rarely as this is heard. The adult is p- ovided with thirty-six, and the young with twenty-four teeth ; in both cases canines appear to be absent ; the median incisors are very long, and project ; there are two-more false grinders in the upper than in the lower jaw, while the true molars of the upper jaw are remarkable for the presence of four cusps, of which the anterior inner and the posterior outer are connected by an obliquely-set ridge. This is the same arrangement as is seen in man. In the lower jaw the corresponding teeth are, as in the lemurs (or half-apes), provided with two transverse ridges.
Sixteen species of the genus have been recognized by some zoologists. The tenrec (Centêtes) of Madagascar has very many points in common with it.