Superficial secondary sexual characters are wanting both in the Hippopotamus and the Camel. Both, however, possess a formidable armature of teeth which are capable of inflicting very severe wounds. In the Hippopotamus the canines are of enormous size, and their punishing power is further strengthened by the fact that they work in opposition to a pair of similar teeth in the lower jaw; they cut like a pair of shears, the upper closing upon the lower pair with the precision of scissors-blades. In addition, the lower jaw develops two long, blunt-pointed, ivory spikes, which are scarcely less to be dreaded. With these weapons the bulls fight furiously, and it is no uncommon thing to find vanquished males frightfully mauled, the hide being lacerated from head to tail. Protection, in a measure, is afforded by its enormous thickness, but the great folds and pleats of skin seen in the Rhinoceros are never developed. The females, however, are similarly armed, and the teeth are nearly as large as in the males, which is a rather unusual occurrence. The Swine, which are near relations of the Hippopotamus, in like manner develop huge pointed canines, and these reach their maximum in the great Wart-hogs of Africa. But in the swine the mechanism differs, for although the canines are closely opposed, the shaft of the upper teeth curves upwards, and the lower teeth are much smaller than the upper. In fighting, these animals do not bite, like the Hippopotamus, but use the upper canines to rip up their antagonist with a sudden, swift upward and sideways movement of the head. How dangerous is the wound thus inflicted those who have hunted the wild-boar know well. A curious exaggeration of this arrangement of the teeth is seen in the Babiroussa. Herein the upper canines grow directly upwards, actually piercing the upper lip as in the case of the downwardly growing tusks of the elephant. That these teeth, however, are of any service in fighting is doubtful, for the upper tooth curves upwards and backwards in a semicircle so that the points are harmless. The tusks of the lower jaw, however, are extremely long and pointed, though their wounding power is limited by reason of the upper teeth. This may account for the fact that the head, the part mostly attacked by enraged boars, presents no sort of armature designed for defence; while in the Wart-hog, on the other hand, great solid bucklers of hide stand out on either side of the head below the eyes, giving the animal a most repulsive appearance, but affording him a very present help in time of trouble. In the wild-boar, where the tusks are shorter, no such protective armature is needed. [Illustration: Plate 10. HEAD OF MALE WART-HOG. In the “Swine” family the canine teeth are always greatly developed, but they attain to their maximum, relatively, in the Wart-hog.] [Illustration: _Photos by Scholastic Photo Co., from “The Living Animals of the World.”_ MALE AND FEMALE BABIRUSA.